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Source — http://www.webopedia.com
http://www.webopedia.com/quick_ref/FileSizeConversionTable.asp
File Size Conversion Table
The table below shows the relationship between the file storage sizes that computers
use. Binary calculations are based on units of 1,024, and decimal calculations are based
on uints of 1,000. It should be noted that decimal calculations are based on units that
have been rounded off to the nearest 1,000 and therefore differ from the actual number
of bytes used in binary calculations.
Name Symbol
Bytes Equal to
kilobyte
KB
megabyte
MB
gigabyte
GB
terabyte
TB
petabyte
PB
exabyte
EB
zettabyte
ZB
yottabyte
YB
November 9, 2003
Binary Measurement
2^10
2^20
2^30
2^40
2^50
2^60
2^70
2^80
10^3
10^6
10^9
10^12
10^15
10^18
10^21
10^24
Decimal Measurement
Number of
1,024 1,024 bytes
1,048,576
1,024KB
1,073,741,824 1,024MB
1,099,511,627,776
1,024GB
1,125,899,906,842,624
1,024TB
1,152,921,504,606,846,976 1,024PB
1,180,591,620,717,411,303,424
1,024EB
1,208,925,819,614,629,174,706,176 1,024ZBLast updated:
access
Last modified: Friday, February 27, 2004
(v.) (1) To use. For example, programs can access memory , which means they read data
from or write data to main memory. A user can access files, directories, computers, or
peripheral devices.
(2) More specifically, access often means to read data from or write data to a mass
storage device. The time it takes to locate a single byte of information on a mass-storage
device is called the access time.
(3) To visit a Web site.
(n.) (1) The act of reading data from or writing data to a storage device.
(2) A privilege to use computer information in some manner. For example, a user might
be granted read access to a file, meaning that the user can read the file but cannot modify
or delete it. Most operating systems have several different types of access privileges that
can be granted or denied to specific users or groups of users.
(3) When capitalized as Access, short for Microsoft Access.
Microsoft Access
Last modified: Friday, February 27, 2004
Often referred to as simply Access, Microsoft’s database creation and management
software.
Access point (yields)
AP
Last modified: Friday, January 16, 2004
Short for Access Point, a hardware device or a computer's software that acts as a
communication hub for users of a wireless device to connect to a wired LAN. APs are
important for providing heightened wireless security and for extending the physical
range of service a wireless user has access to.
Also see infrastructure mode and ad-hoc mode.
Also see the Wireless LAN Standards chart in the Quick Reference section of
Webopedia
Acquistion cost (yields)
cost per thousand
Last modified: Thursday, August 21, 2003
Abbreviated as CPM (the letter "M" in the abbreviation is the Roman numeral for one
thousand). CPM is used by Internet marketers to price ad banners. Sites that sell
advertising will guarantee an advertiser a certain number of impressions (number of
times an ad banner is downloaded and presumably seen by visitors.), then set a rate
based on that guarantee times the CPM rate. A Web site that has a CPM rate of $25 and
guarantees advertisers 600,000 impressions will charge $15,000 ($25 x 600) for those
advertisers' ad banner.
ANSI
Last modified: Friday, June 22, 2001
Acronym for the American National Standards Institute. Founded in 1918, ANSI is a
voluntary organization composed of over 1,300 members (including all the large
computer companies) that creates standards for the computer industry. For example,
ANSI C is a version of the C language that has been approved by the ANSI committee.
To a large degree, all ANSI C compilers, regardless of which company produces them,
should behave similarly.
In addition to programming languages, ANSI sets standards for a wide range of
technical areas, from electrical specifications to communications protocols. For example,
FDDI, the main set of protocols for sending data over fiber optic cables, is an ANSI
standard.
Apache (yields)
Apache Web server
Last modified: Tuesday, March 11, 2003
Often referred to as simply Apache, a public-domain open source Web server developed
by a loosely-knit group of programmers. The first version of Apache, based on the
NCSA httpd Web server, was developed in 1995.
Core development of the Apache Web server is performed by a group of about 20
volunteer programmers, called the Apache Group. However, because the source code is
freely available, anyone can adapt the server for specific needs, and there is a large
public library of Apache add-ons. In many respects, development of Apache is similar
to development of the Linux operating system.
The original version of Apache was written for UNIX, but there are now versions that
run under OS/2, Windows and other platforms.
The name is a tribute to the Native American Apache Indian tribe, a tribe well known
for its endurance and skill in warfare. A common misunderstanding is that it was called
Apache because it was developed from existing NCSA code plus various patches, hence
the name a patchy server, or Apache server.
application server
Last modified: Tuesday, January 28, 2003
Also called an appserver. A program that handles all application operations between
users and an organization's backend business applications or databases. Application
servers are typically used for complex transaction-based applications. To support highend needs, an application server has to have built-in redundancy, monitors for highavailability, high-performance distributed application services and support for complex
database access.
See the Server Types page in the quick reference section of Webopedia for a comparison
of server types.
(Many thanks go out to Paul White, Product Marketing Manager EMEA, BEA Systems, for
providing this updated definition.)
ARPANET
Last modified: Monday, July 02, 2001
The precursor to the Internet, ARPANET was a large wide-area network created by the
United States Defense Advanced Research Project Agency (ARPA). Established in 1969,
ARPANET served as a testbed for new networking technologies, linking many
universities and research centers. The first two nodes that formed the ARPANET were
UCLA and the Stanford Research Institute, followed shortly thereafter by the University
of Utah.
ASCII
Last modified: Monday, August 05, 2002
Acronym for the American Standard Code for Information Interchange. Pronounced ask-ee,
ASCII is a code for representing English characters as numbers, with each letter
assigned a number from 0 to 127. For example, the ASCII code for uppercase M is 77.
Most computers use ASCII codes to represent text, which makes it possible to transfer
data from one computer to another.
For a list of commonly used characters and their ASCII equivalents, refer to the ASCII
page in the Quick Reference section.
Text files stored in ASCII format are sometimes called ASCII files. Text editors and
word processors are usually capable of storing data in ASCII format, although ASCII
format is not always the default storage format. Most data files, particularly if they
contain numeric data, are not stored in ASCII format. Executable programs are never
stored in ASCII format.
The standard ASCII character set uses just 7 bits for each character. There are several
larger character sets that use 8 bits, which gives them 128 additional characters. The
extra characters are used to represent non-English characters, graphics symbols, and
mathematical symbols. Several companies and organizations have proposed extensions
for these 128 characters. The DOS operating system uses a superset of ASCII called
extended ASCII or high ASCII. A more universal standard is the ISO Latin 1 set of
characters, which is used by many operating systems, as well as Web browsers.
Another set of codes that is used on large IBM computers is EBCDIC.
backup
Last modified: Tuesday, May 25, 2004
(v.) To copy files to a second medium (a disk or tape) as a precaution in case the first
medium fails. One of the cardinal rules in using computers is back up your files regularly.
Even the most reliable computer is apt to break down eventually. Many professionals
recommend that you make two, or even three, backups of all your files. To be especially
safe, you should keep one backup in a different location from the others.
You can back up files using operating system commands, or you can buy a specialpurpose backup utility. Backup programs often compress the data so that backups
require fewer disks.
(n.) (1) The act of backing up.
(2) A substitute or alternative. The term backup usually refers to a disk or tape that
contains a copy of data.
binary
Last modified: Friday, March 21, 2003
Pertaining to a number system that has just two unique digits. For most purposes, we
use the decimal number system, which has ten unique digits, 0 through 9. All other
numbers are then formed by combining these ten digits. Computers are based on the
binary numbering system, which consists of just two unique numbers, 0 and 1. All
operations that are possible in the decimal system (addition, subtraction, multiplication,
division) are equally possible in the binary system.
We use the decimal system in everyday life because it seems more natural (we have ten
fingers and ten toes). For the computer, the binary system is more natural because of its
electrical nature (charged versus uncharged).
In the decimal system, each digit position represents a value of 10 to the position's
power. For example, the number 345 means:
3 three 100s (10 to the 2nd power)
plus
4 four 10s (10 to the first power)
plus
5 five 1s (10 to the zeroth power)
In the binary system, each digit position represents a value of 2. For example, the binary
number 1011 equals:
1 one 8 (2 to the 3rd power)
plus
0 zero 4s (2 to the 2nd power)
plus
1 one 2 (2 to the first power)
plus
1 one 1 (2 to the zeroth power)
So a binary 1011 equals a decimal 11.
Because computers use the binary number system, powers of 2 play an important role.
This is why everything in computers seems to come in 8s (2 to the 3rd power), 64s (2 to
the 6th power), 128s (2 to the 7th power), and 256s (2 to the 8th power).
Programmers also use the octal (8 numbers) and hexadecimal (16 numbers) number
systems because they map nicely onto the binary system. Each octal digit represents
exactly three binary digits, and each hexadecimal digit represents four binary digits.
bit
Last modified: Tuesday, August 03, 2004
Short for binary digit, the smallest unit of information on a machine. The term was first
used in 1946 by John Tukey, a leading statistician and adviser to five presidents. A
single bit can hold only one of two values: 0 or 1. More meaningful information is
obtained by combining consecutive bits into larger units. For example, a byte is
composed of 8 consecutive bits.
Computers are sometimes classified by the number of bits they can process at one time
or by the number of bits they use to represent addresses. These two values are not
always the same, which leads to confusion. For example, classifying a computer as a 32bit machine might mean that its data registers are 32 bits wide or that it uses 32 bits to
identify each address in memory. Whereas larger registers make a computer faster,
using more bits for addresses enables a machine to support larger programs.
Graphics are also often described by the number of bits used to represent each dot. A 1bit image is monochrome; an 8-bit image supports 256 colors or grayscales; and a 24- or
32-bit graphic supports true color.
blog
Last modified: Monday, March 08, 2004
(n.) Short for Web log, a blog is a Web page that serves as a publicly accessible personal
journal for an individual. Typically updated daily, blogs often reflect the personality of
the author.
(v.) To author a Web log.
Other forms: Blogger (a person who blogs).
byte
Last modified: Tuesday, May 21, 2002
Abbreviation for binary term, a unit of storage capable of holding a single character. On
almost all modern computers, a byte is equal to 8 bits. Large amounts of memory are
indicated in terms of kilobytes (1,024 bytes), megabytes (1,048,576 bytes), and gigabytes
(1,073,741,824 bytes).
server blade
Last modified: Monday, August 05, 2002
A single circuit board populated with components such as processors, memory, and
network connections that are usually found on multiple boards. Server blades are
designed to slide into existing servers. Server blades are more cost-efficient, smaller and
consume less power than traditional box-based servers.
Also see the Server Types page in the Quick Reference section of Webopedia for a
comparison of server types.
bps
Last modified: Tuesday, May 21, 2002
Abbreviation of bits per second, the standard measure of data transmission speeds.
broadband
Last modified: Tuesday, June 15, 2004
A type of data transmission in which a single medium (wire) can carry several channels
at once. Cable TV, for example, uses broadband transmission. In contrast, baseband
transmission allows only one signal at a time.
Most communications between computers, including the majority of local-area
networks, use baseband communications. An exception is B-ISDN networks, which
employ broadband transmission.
CERN
Last modified: Wednesday, January 22, 2003
Pronounced sern. Short for Conseil Europeen pour le Recherche Nucleaire (European
Laboratory for Particle Physics), a research laboratory headquartered in Geneva,
Switzerland, and funded by many different countries. While most work deals with
nuclear physics, the CERN is known for Tim Berners-Lee's pioneering work in
developing the World Wide Web portion of the Internet.
CGI
Last modified: Tuesday, March 02, 2004
Abbreviation of Common Gateway Interface, a specification for transferring information
between a World Wide Web server and a CGI program. A CGI program is any program
designed to accept and return data that conforms to the CGI specification. The program
could be written in any programming language, including C, Perl, Java, or Visual Basic.
CGI programs are the most common way for Web servers to interact dynamically with
users. Many HTML pages that contain forms, for example, use a CGI program to
process the form's data once it's submitted. Another increasingly common way to
provide dynamic feedback for Web users is to include scripts or programs that run on
the user's machine rather than the Web server. These programs can be Java applets, Java
scripts, or ActiveX controls. These technologies are known collectively as client-side
solutions, while the use of CGI is a server-side solution because the processing occurs on
the Web server.
One problem with CGI is that each time a CGI script is executed, a new process is
started. For busy Web sites, this can slow down the server noticeably. A more efficient
solution, but one that it is also more difficult to implement, is to use the server's API,
such as ISAPI or NSAPI. Another increasingly popular solution is to use Java servlets.
click-through
Last modified: Tuesday, February 11, 2003
The process of a visitor clicking on a Web advertisement and going to the advertiser's
Web site. Also called ad clicks or requests. The click rate measures the amount of times
an ad is clicked versus the amount of times it's viewed.
client
(klÄ«´&nt) (n.) The client part of a client-server architecture. Typically, a client is an
application that runs on a personal computer or workstation and relies on a server to
perform some operations. For example, an e-mail client is an application that enables
you to send and receive e-mail.
coaxial cable
Last modified: Thursday, March 27, 2003
A type of wire that consists of a center wire surrounded by insulation and then a
grounded shield of braided wire. The shield minimizes electrical and radio frequency
interference.
Coaxial cabling is the primary type of cabling used by the cable television industry and
is also widely used for computer networks, such as Ethernet. Although more expensive
than standard telephone wire, it is much less susceptible to interference and can carry
much more data.
cookie
Last modified: Monday, November 03, 2003
A message given to a Web browser by a Web server. The browser stores the message in
a text file. The message is then sent back to the server each time the browser requests a
page from the server.
Also see session cookie and persistent cookie.
The main purpose of cookies is to identify users and possibly prepare customized Web
pages for them. When you enter a Web site using cookies, you may be asked to fill out a
form providing such information as your name and interests. This information is
packaged into a cookie and sent to your Web browser which stores it for later use. The
next time you go to the same Web site, your browser will send the cookie to the Web
server. The server can use this information to present you with custom Web pages. So,
for example, instead of seeing just a generic welcome page you might see a welcome
page with your name on it.
The name cookie derives from UNIX objects called magic cookies. These are tokens that
are attached to a user or program and change depending on the areas entered by the
user or program.
Also see Do Cookies Compromise Security? in the Did You Know . . . ? section of
Webopedia.
CPC
Last modified: Thursday, July 24, 2003
Short for cost-per-click, an Internet marketing formula used to price online
advertisements. Advertisers will pay Internet publishers based on the number of clicks
a specific ad gets.
CPM
Last modified: Thursday, August 21, 2003
(1) Short for Critical Path Method.
(2) Short for cost per thousand.
Also see CP/M.
CP/M
Last modified: Friday, January 31, 2003
Abbreviation of Control Program for Microcomputers. Created by Digital Research
Corporation, CP/M was one of the first 8-bit operating systems for personal computers.
However, Digital Research Corporation made a critical strategic error by not agreeing to
produce an operating system for the first IBM PC. According to the folklore, the
president of Digital Research was flying his airplane when IBM came to call. IBM
marched out and never looked back.
Instead, IBM turned to Microsoft Corporation, which developed MS-DOS based on
version 2.2 of CP/M. By the mid 1980s, MS-DOS had become the standard operating
system for IBM-compatible personal computers. CP/M is now obsolete.
CPU
Last modified: Wednesday, January 15, 2003
Abbreviation of central processing unit, and pronounced as separate letters. The CPU is
the brains of the computer. Sometimes referred to simply as the processor or central
processor, the CPU is where most calculations take place. In terms of computing power,
the CPU is the most important element of a computer system.
On large machines, CPUs require one or more printed circuit boards. On personal
computers and small workstations, the CPU is housed in a single chip called a
microprocessor.
Two typical components of a CPU are:
*
The arithmetic logic unit (ALU), which performs arithmetic and logical operations.
*
The control unit, which extracts instructions from memory and decodes and
executes them, calling on the ALU when necessary.
CRM
Last modified: Thursday, July 24, 2003
Short for customer relationship management. CRM entails all aspects of interaction a
company has with its customer, whether it be sales or service related. Computerization
has changed the way companies are approaching their CRM strategies because it has
also changed consumer buying behavior. With each new advance in technology,
especially the proliferation of self-service channels like the Web and WAP phones, more
of the relationship is being managed electronically. Organizations are therefore looking
for ways to personalize online experiences (a process also referred to as mass
customization) through tools such as help-desk software, e-mail organizers and Web
development apps.
cryptography
Last modified: Tuesday, March 16, 2004
The art of protecting information by transforming it (encrypting it) into an unreadable
format, called cipher text. Only those who possess a secret key can decipher (or decrypt)
the message into plain text. Encrypted messages can sometimes be broken by
cryptanalysis, also called codebreaking, although modern cryptography techniques are
virtually unbreakable.
As the Internet and other forms of electronic communication become more prevalent,
electronic security is becoming increasingly important. Cryptography is used to protect
e-mail messages, credit card information, and corporate data. One of the most popular
cryptography systems used on the Internet is Pretty Good Privacy because it's effective
and free.
Cryptography systems can be broadly classified into symmetric-key systems that use a
single key that both the sender and recipient have, and public-key systems that use two
keys, a public key known to everyone and a private key that only the recipient of
messages uses.
daemon
Last modified: Tuesday, April 22, 2003
Pronounced DEE-mun or DAY-mun. A process that runs in the background and
performs a specified operation at predefined times or in response to certain events. The
term daemon is a UNIX term, though many other operating systems provide support for
daemons, though they're sometimes called other names. Windows, for example, refers
to daemons as System Agents and services.
Typical daemon processes include print spoolers, e-mail handlers, and other programs
that perform administrative tasks for the operating system. The term comes from Greek
mythology, where daemons were guardian spirits.
data mining
Last modified: Monday, December 02, 2002
A class of database applications that look for hidden patterns in a group of data that
can be used to predict future behavior. For example, data mining software can help
retail companies find customers with common interests. The term is commonly misused
to describe software that presents data in new ways. True data mining software doesn't
just change the presentation, but actually discovers previously unknown relationships
among the data.
Data mining is popular in the science and mathematical fields but also is utilized
increasingly by marketers trying to distill useful consumer data from Web sites.
database
Last modified: Friday, June 27, 2003
(1) Often abbreviated DB. A collection of information organized in such a way that a
computer program can quickly select desired pieces of data. You can think of a database
as an electronic filing system.
Traditional databases are organized by fields, records, and files. A field is a single piece of
information; a record is one complete set of fields; and a file is a collection of records.
For example, a telephone book is analogous to a file. It contains a list of records, each of
which consists of three fields: name, address, and telephone number.
An alternative concept in database design is known as Hypertext. In a Hypertext
database, any object, whether it be a piece of text, a picture, or a film, can be linked to
any other object. Hypertext databases are particularly useful for organizing large
amounts of disparate information, but they are not designed for numerical analysis.
To access information from a database, you need a database management system (DBMS).
This is a collection of programs that enables you to enter, organize, and select data in a
database.
(2) Increasingly, the term database is used as shorthand for database management system.
DNS
Last modified: Tuesday, March 23, 2004
(1) Short for Domain Name System (or Service or Server), an Internet service that
translates domain names into IP addresses. Because domain names are alphabetic, they're
easier to remember. The Internet however, is really based on IP addresses. Every time
you use a domain name, therefore, a DNS service must translate the name into the
corresponding IP address. For example, the domain name www.example.com might
translate to 198.105.232.4.
The DNS system is, in fact, its own network. If one DNS server doesn't know how to
translate a particular domain name, it asks another one, and so on, until the correct IP
address is returned.
(2) Short for digital nervous system, a term coined by Bill Gates to describe a network of
personal computers that make it easier to obtain and understand information.
DOS
Last modified: Friday, December 14, 2001
(1) Acronym for disk operating system. The term DOS can refer to any operating system,
but it is most often used as a shorthand for MS-DOS (Microsoft disk operating system).
Originally developed by Microsoft for IBM, MS-DOS was the standard operating
system for IBM-compatible personal computers.
The initial versions of DOS were very simple and resembled another operating system
called CP/M. Subsequent versions have became increasingly sophisticated as they
incorporated features of minicomputer operating systems. However, DOS is still a 16bit operating system and does not support multiple users or multitasking.
For some time, it has been widely acknowledged that DOS is insufficient for modern
computer applications. Microsoft Windows helped alleviate some problems, but still, it
sat on top of DOS and relied on DOS for many services. Even Windows 95 sat on top of
DOS. Newer operating systems, such as Windows NT and OS/2 Warp, do not rely on
DOS to the same extent, although they can execute DOS-based programs. It is expected
that as these operating systems gain market share, DOS will eventually disappear. In
the meantime, Caldera, Inc. markets a version of DOS called DR-OpenDOS that extends
MS-DOS in significant ways.
(2) See DoS attack.
dpi
Last modified: Tuesday, May 21, 2002
Abbreviation of dots per inch, which indicates the resolution of images. The more dots
per inch, the higher the resolution. A common resolution for laser printers is 600 dots
per inch. This means 600 dots across and 600 dots down, so there are 360,000 dots per
square inch.
DRAM
Last modified: Thursday, June 12, 2003
Pronounced dee-ram, DRAM stands for dynamic random access memory, a type of
memory used in most personal computers.
dumb terminal
Last modified: Sunday, September 01, 1996
A display monitor that has no processing capabilities. A dumb terminal is simply an
output device that accepts data from the CPU. In contrast, a smart terminal is a monitor
that has its own processor for special features, such as bold and blinking characters.
Dumb terminals are not as fast as smart terminals, and they do not support as many
display features, but they are adequate for most applications.
easter egg
Last modified: Tuesday, September 24, 2002
A secret message or screen buried in an application. Typically, easter eggs are used to
display the credits for the development team or to display a humorous message. To see
an easter egg, you need to know a special procedure or sequence of keystrokes.
For example, follow these instructions to see a list of people who worked on the User
Assistance feature of Microsoft Word 2000:
1. Open Microsoft Word2000
2. Press F1 or click the "Office Assistant" button
3. Under the "What would you like to do?", type "Cast" (No quotes)
4. Click SEARCH
5. Click the MICROSOFT OFFICE 2000 USER ASSISTANCE STAFF topic
6. Click the graphic in the Microsoft Word Help screen
Ethernet
Last modified: Tuesday, February 18, 2003
A local-area network (LAN) architecture developed by Xerox Corporation in
cooperation with DEC and Intel in 1976. Ethernet uses a bus or star topology and
supports data transfer rates of 10 Mbps. The Ethernet specification served as the basis
for the IEEE 802.3 standard, which specifies the physical and lower software layers.
Ethernet uses the CSMA/CD access method to handle simultaneous demands. It is one
of the most widely implemented LAN standards.
A newer version of Ethernet, called 100Base-T (or Fast Ethernet), supports data transfer
rates of 100 Mbps. And the newest version, Gigabit Ethernet supports data rates of 1
gigabit (1,000 megabits) per second.
Also see the Ethernet Designations chart in the Quick Reference section of Webopedia.
firewall
Last modified: Tuesday, August 03, 2004
(f¥r´wâl) (n.) A system designed to prevent unauthorized access to or from a private
network. Firewalls can be implemented in both hardware and software, or a
combination of both. Firewalls are frequently used to prevent unauthorized Internet
users from accessing private networks connected to the Internet, especially intranets. All
messages entering or leaving the intranet pass through the firewall, which examines
each message and blocks those that do not meet the specified security criteria.
There are several types of firewall techniques:
*
Packet filter: Looks at each packet entering or leaving the network and accepts
or rejects it based on user-defined rules. Packet filtering is fairly effective and
transparent to users, but it is difficult to configure. In addition, it is susceptible to IP
spoofing.
*
Application gateway: Applies security mechanisms to specific applications, such
as FTP and Telnet servers. This is very effective, but can impose a performance
degradation.
*
Circuit-level gateway: Applies security mechanisms when a TCP or UDP
connection is established. Once the connection has been made, packets can flow
between the hosts without further checking.
*
Proxy server: Intercepts all messages entering and leaving the network. The
proxy server effectively hides the true network addresses.
In practice, many firewalls use two or more of these techniques in concert.
A firewall is considered a first line of defense in protecting private information. For
greater security, data can be encrypted.
FLOPS
Last modified: Tuesday, October 30, 2001
Short for floating-point operations per second, a common benchmark measurement for
rating the speed of microprocessors. Floating-point operations include any operations
that involve fractional numbers. Such operations, which take much longer to compute
than integer operations, occur often in some applications.
Most modern microprocessors include a floating-point unit (FPU), which is a
specialized part of the microprocessor responsible for executing floating-point
operations. The FLOPS measurement, therefore, actually measures the speed of the
FPU. One of the most common benchmark tests used to measure FLOPS is called
Linpack.
Many experts feel that FLOPS is not a relevant measurement because it fails to take into
account factors such as the condition under which the microprocessor is running (e.g.,
heavy or light loads) and which exact operations are included as floating-point
operations. For this reason, a consortium of vendors created the Standard Performance
Evaluation Corporation (SPEC), which provides more meaningful benchmark values.
A megaFLOPS (MFLOPS) is equal to one million floating-point operations per second,
and a gigaFLOPS (GFLOPS) is equal to one billion floating-point operations per second.
fps
Last modified: Monday, August 02, 2004
(pronounced as separate letters) Short for frames per second (and typically written in lower
case), a measure of how much information is used to store and display motion video.
The term applies equally to film video and digital video. Each frame is a still image;
displaying frames in quick succession creates the illusion of motion. The more frames
per second (fps), the smoother the motion appears. Television in the U.S., for example,
is based on the NTSC format, which displays 30 interlaced frames per second (60 fields
per second). In general, the minimum fps needed to avoid jerky motion is about 30. Some
computer video formats, such as AVI, provide only 15 frames per second.
fractal
Last modified: Sunday, September 01, 1996
A word coined by Benoit Mandelbrot in 1975 to describe shapes that are "self-similar" -that is, shapes that look the same at different magnifications. To create a fractal, you
start with a simple shape and duplicate it successively according to a set of fixed rules.
Oddly enough, such a simple formula for creating shapes can produce very complex
structures, some of which have a striking resemblance to objects that appear in the real
world. For example, graphics designers use fractals to generate images of mountainous
landscapes, coastlines, and flowers. In fact, many of the computer -generated images
that appear in science fiction films utilize fractals.
FORTRAN
Last modified: Tuesday, May 19, 1998
Acronym for formula translator, FORTRAN is the oldest high-level programming
language. Designed by John Backus for IBM in the late 1950s, it is still popular today,
particularly for scientific applications that require extensive mathematical
computations.
The two most common versions of FORTRAN are FORTRAN IV and FORTRAN 77.
FORTRAN IV was approved as a USASI standard in 1966. FORTRAN 77 is a version of
FORTRAN that was approved by ANSI in 1978 (they had expected to approve it in
1977, hence the name). FORTRAN 77 includes a number of features not available in
older versions of FORTRAN. A new ISO and ANSI standard for FORTRAN, called
FORTRAN-90, was developed in the early 90s.
front end
Last modified: Friday, November 01, 1996
(1) For software applications, front end is the same as user interface.
(2) In client/server applications, the client part of the program is often called the front
end and the server part is called the back end.
(3) Compilers, the programs that translate source code into object code, are often
composed of two parts: a front end and a back end. The front end is responsible for
checking syntax and detecting errors, whereas the back end performs the actual
translation into object code.
FTP
Last modified: Wednesday, July 21, 2004
Short for File Transfer Protocol, the protocol for exchanging files over the Internet. FTP
works in the same way as HTTP for transferring Web pages from a server to a user's
browser and SMTP for transferring electronic mail across the Internet in that, like these
technologies, FTP uses the Internet's TCP/IP protocols to enable data transfer.
FTP is most commonly used to download a file from a server using the Internet or to
upload a file to a server (e.g., uploading a Web page file to a server).
GIF
Last modified: Monday, May 05, 2003
Pronounced jiff or giff (hard g) stands for graphics interchange format, a bit-mapped
graphics file format used by the World Wide Web, CompuServe and many BBSs. GIF
supports color and various resolutions. It also includes data compression, but because it
is limited to 256 colors, it is more effective for scanned images such as illustrations
rather than color photos.
GPS
Last modified: Wednesday, September 25, 2002
Short for Global Positioning System, a worldwide MEO satellite navigational system
formed by 24 satellites orbiting the earth and their corresponding receivers on the earth.
The satellites orbit the earth at approximately 12,000 miles above the surface and make
two complete orbits every 24 hours. The GPS satellites continuously transmit digital
radio signals that contain data on the satellites location and the exact time to the earthbound receivers. The satellites are equipped with atomic clocks that are precise to
within a billionth of a second. Based on this information the receivers know how long it
takes for the signal to reach the receiver on earth. As each signal travels at the speed of
light, the longer it takes the receiver to get the signal, the farther away the satellite is. By
knowing how far away a satellite is, the receiver knows that it is located somewhere on
the surface of an imaginary sphere centered at the satellite. By using three satellites,
GPS can calculate the longitude and latitude of the receiver based on where the three
spheres intersect. By using four satellites, GPS can also determine altitude.
GPS was developed and is operated by the U.S. Department of Defense. It was
originally called NAVSTAR (Navigation System with Timing and Ranging). Before its
civilian applications, GPS was used to provide all-weather round-the-clock navigation
capabilities for military ground, sea, and air forces.
GPS has applications beyond navigation and location determination. GPS can be used
for cartography, forestry, mineral exploration, wildlife habitation management,
monitoring the movement of people and things and bringing precise timing to the
world.
GUI
Last modified: Wednesday, January 22, 2003
Pronounced GOO-ee. Acronym for graphical user interface.
HTML
Last modified: Monday, June 14, 2004
Short for HyperText Markup Language, the authoring language used to create documents
on the World Wide Web. HTML is similar to SGML, although it is not a strict subset.
HTML defines the structure and layout of a Web document by using a variety of tags
and attributes. The correct structure for an HTML document starts with
<HTML><HEAD>(enter here what document is about) and ends with
</BODY></HTML>. All the information you'd like to include in your Web page fits in
between the <BODY> and </BODY> tags.
There are hundreds of other tags used to format and layout the information in a Web
page. Tags are also used to specify hypertext links. These allow Web developers to
direct users to other Web pages with only a click of the mouse on either an image or
word(s). For a more complete list of tags, check out some of the URLs below.
IEEE
Last modified: Monday, July 19, 2004
Abbreviation of Institute of Electrical and Electronics Engineers, pronounced I-triple-E.
Founded in 1884 as the AIEE, the IEEE was formed in 1963 when AIEE merged with
IRE. IEEE is an organization composed of engineers, scientists, and students. The IEEE
is best known for developing standards for the computer and electronics industry. In
particular, the IEEE 802 standards for local-area networks are widely followed.
impression
Last modified: Tuesday, February 11, 2003
An advertisement's appearance on an accessed Web page. For example, if the page
you're on shows three ads, that's three impressions. Advertisers use impressions to
measure the number of views their ads receive, and publishers often sell ad space
according to impressions. (It can be tough to know, though, whether an impression
really means a visitor saw the ad, since they could be browsing without graphics or
might not have scrolled down far enough.) Impressions are tracked in a log maintained
by a site server and are often sold on a cost per thousand (CPM) basis.
Intel
Last modified: Thursday, November 08, 2001
The world's largest manufacturer of computer chips. Although it has been challenged
in recent years by newcomers AMD and Cyrix, Intel still dominates the market for PC
microprocessors. Nearly all PCs are based on Intel's x86 architecture.
Intel was founded in 1968 by Bob Noyce and Gordon Moore. Strategically, it is closely
allied with Microsoft because the Windows 3.x and 95 operating systems are designed
for x86 microprocessors. The popularity of Windows creates a demand for Intel or Intelcompatible microprocessors. Many people refer to this alliance as Wintel (short for
Windows-Intel).
InterNIC
Last modified: Thursday, January 08, 2004
Short for Internet Network Information Center, a registered service mark of the U.S.
Department of Commerce and now a defunct entity. InterNIC began as a collaborative
project between AT&T and Network Solutions, Inc. (NSI) supported by the National
Science Foundation. When active, the project offered four services:
*
InterNIC Directory and Database Services -- online white pages directory and
directory of publicly accessible databases managed by AT&T.
*
Registration Services -- domain name and IP address assignment managed by
NSI.
*
Support Services -- outreach, education, and information services for the Internet
community managed by NSI.
*
Net Scout Services -- online publications that summarize recent happenings of
interest to Internet users (managed by NSI).
The InterNIC is currently an informational Web site established to provide the public
with information about domain name registration. ICANN now oversees the domain
name registration industry.
IP
Last modified: Monday, June 07, 2004
Abbreviation of Internet Protocol, pronounced as two separate letters. IP specifies the
format of packets, also called datagrams, and the addressing scheme. Most networks
combine IP with a higher-level protocol called Transmission Control Protocol (TCP),
which establishes a virtual connection between a destination and a source.
IP by itself is something like the postal system. It allows you to address a package and
drop it in the system, but there's no direct link between you and the recipient. TCP/IP,
on the other hand, establishes a connection between two hosts so that they can send
messages back and forth for a period of time.
The current version of IP is IPv4. A new version, called IPv6 or IPng, is under
development.
ISDN
Last modified: Monday, July 28, 2003
Abbreviation of integrated services digital network, an international communications
standard for sending voice, video, and data over digital telephone lines or normal
telephone wires. ISDN supports data transfer rates of 64 Kbps (64,000 bits per second).
There are two types of ISDN:
*
Basic Rate Interface (BRI) -- consists of two 64-Kbps B-channels and one Dchannel for transmitting control information.
*
Primary Rate Interface (PRI) -- consists of 23 B-channels and one D-channel (U.S.)
or 30 B-channels and one D-channel (Europe).
The original version of ISDN employs baseband transmission. Another version, called
B-ISDN, uses broadband transmission and is able to support transmission rates of 1.5
Mbps. B-ISDN requires fiber optic cables and is not widely available.
ISP
Last modified: Friday, March 12, 2004
Short for Internet Service Provider, a company that provides access to the Internet. For a
monthly fee, the service provider gives you a software package, username, password
and access phone number. Equipped with a modem, you can then log on to the Internet
and browse the World Wide Web and USENET, and send and receive e-mail.
In addition to serving individuals, ISPs also serve large companies, providing a direct
connection from the company's networks to the Internet. ISPs themselves are connected
to one another through Network Access Points (NAPs).
ISPs are also called IAPs (Internet Access Providers).
Java
Last modified: Thursday, May 01, 2003
A high-level programming language developed by Sun Microsystems. Java was
originally called OAK, and was designed for handheld devices and set-top boxes. Oak
was unsuccessful so in 1995 Sun changed the name to Java and modified the language
to take advantage of the burgeoning World Wide Web.
Java is an object-oriented language similar to C++, but simplified to eliminate language
features that cause common programming errors. Java source code files (files with a
.java extension) are compiled into a format called bytecode (files with a .class extension),
which can then be executed by a Java interpreter. Compiled Java code can run on most
computers because Java interpreters and runtime environments, known as Java Virtual
Machines (VMs), exist for most operating systems, including UNIX, the Macintosh OS,
and Windows. Bytecode can also be converted directly into machine language
instructions by a just-in-time compiler (JIT).
Java is a general purpose programming language with a number of features that make
the language well suited for use on the World Wide Web. Small Java applications are
called Java applets and can be downloaded from a Web server and run on your
computer by a Java-compatible Web browser, such as Netscape Navigator or Microsoft
Internet Explorer.
JPEG
Last modified: Monday, May 05, 2003
Short for Joint Photographic Experts Group, and pronounced jay-peg. JPEG is a lossy
compression technique for color images. Although it can reduce files sizes to about 5% of
their normal size, some detail is lost in the compression.
Also see JPG vs. GIF vs. PNG in the Did You Know . . . ? section of Webopedia.
LAN (yields)
local-area network
Last modified: Tuesday, February 18, 2003
A computer network that spans a relatively small area. Most LANs are confined to a
single building or group of buildings. However, one LAN can be connected to other
LANs over any distance via telephone lines and radio waves. A system of LANs
connected in this way is called a wide-area network (WAN).
Most LANs connect workstations and personal computers. Each node (individual
computer ) in a LAN has its own CPU with which it executes programs, but it also is
able to access data and devices anywhere on the LAN. This means that many users can
share expensive devices, such as laser printers, as well as data. Users can also use the
LAN to communicate with each other, by sending e-mail or engaging in chat sessions.
There are many different types of LANs Ethernets being the most common for PCs. Most
Apple Macintosh networks are based on Apple's AppleTalk network system, which is
built into Macintosh computers.
The following characteristics differentiate one LAN from another:
*
topology : The geometric arrangement of devices on the network. For example,
devices can be arranged in a ring or in a straight line.
*
protocols : The rules and encoding specifications for sending data. The protocols
also determine whether the network uses a peer-to-peer or client/server architecture.
*
media : Devices can be connected by twisted-pair wire, coaxial cables, or fiber
optic cables. Some networks do without connecting media altogether, communicating
instead via radio waves.
LANs are capable of transmitting data at very fast rates, much faster than data can be
transmitted over a telephone line; but the distances are limited, and there is also a limit
on the number of computers that can be attached to a single LAN.
LCD
Last modified: Wednesday, June 02, 2004
Short for liquid crystal display, a type of display used in digital watches and many
portable computers. LCD displays utilize two sheets of polarizing material with a liquid
crystal solution between them. An electric current passed through the liquid causes the
crystals to align so that light cannot pass through them. Each crystal, therefore, is like a
shutter, either allowing light to pass through or blocking the light.
Monochrome LCD images usually appear as blue or dark gray images on top of a
grayish-white background. Color LCD displays use two basic techniques for producing
color: Passive matrix is the less expensive of the two technologies. The other technology,
called thin film transistor (TFT) or active-matrix, produces color images that are as sharp
as traditional CRT displays, but the technology is expensive. Recent passive-matrix
displays using new CSTN and DSTN technologies produce sharp colors rivaling activematrix displays.
Most LCD screens used in notebook computers are backlit, or transmissive, to make
them easier to read.
Linux
Last modified: Wednesday, April 28, 2004
Pronounced lee-nucks or lih-nucks. A freely-distributable open source operating system
that runs on a number of hardware platforms. The Linux kernel was developed mainly
by Linus Torvalds. Because it's free, and because it runs on many platforms, including
PCs and Macintoshes, Linux has become an extremely popular alternative to
proprietary operating systems.
log file
Last modified: Tuesday, March 12, 2002
A file that lists actions that have occurred. For example, Web servers maintain log files
listing every request made to the server. With log file analysis tools, it's possible to get a
good idea of where visitors are coming from, how often they return, and how they
navigate through a site. Using cookies enables Webmasters to log even more detailed
information about how individual users are accessing a site.
mainframe
Last modified: Monday, October 14, 2002
A very large and expensive computer capable of supporting hundreds, or even
thousands, of users simultaneously. In the hierarchy that starts with a simple
microprocessor (in watches, for example) at the bottom and moves to supercomputers
at the top, mainframes are just below supercomputers. In some ways, mainframes are
more powerful than supercomputers because they support more simultaneous
programs. But supercomputers can execute a single program faster than a mainframe.
The distinction between small mainframes and minicomputers is vague, depending
really on how the manufacturer wants to market its machines.
middleware
Last modified: Friday, June 04, 2004
Software that connects two otherwise separate applications. For example, there are a
number of middleware products that link a database system to a Web server. This
allows users to request data from the database using forms displayed on a Web
browser, and it enables the Web server to return dynamic Web pages based on the
user's requests and profile.
The term middleware is used to describe separate products that serve as the glue
between two applications. It is, therefore, distinct from import and export features that
may be built into one of the applications. Middleware is sometimes called plumbing
because it connects two sides of an application and passes data between them. Common
middleware categories include:
*
*
*
*
*
*
*
ESBs
TP monitors
DCE environments
RPC systems
Object Request Brokers (ORBs)
Database access systems
Message Passing
MIDI
Last modified: Friday, May 16, 2003
Pronounced middy, an acronym for musical instrument digital interface, a standard
adopted by the electronic music industry for controlling devices, such as synthesizers
and sound cards, that emit music. At minimum, a MIDI representation of a sound
includes values for the note's pitch, length, and volume. It can also include additional
characteristics, such as attack and delay time.
The MIDI standard is supported by most synthesizers, so sounds created on one
synthesizer can be played and manipulated on another synthesizer. Computers that
have a MIDI interface can record sounds created by a synthesizer and then manipulate
the data to produce new sounds. For example, you can change the key of a composition
with a single keystroke.
A number of software programs are available for composing and editing music that
conforms to the MIDI standard. They offer a variety of functions: for instance, when
you play a tune on a keyboard connected to a computer, a music program can translate
what you play into a written score.
Moore's Law
Last modified: Sunday, March 22, 1998
The observation made in 1965 by Gordon Moore, co-founder of Intel, that the number
of transistors per square inch on integrated circuits had doubled every year since the
integrated circuit was invented. Moore predicted that this trend would continue for the
foreseeable future. In subsequent years, the pace slowed down a bit, but data density
has doubled approximately every 18 months, and this is the current definition of
Moore's Law, which Moore himself has blessed. Most experts, including Moore himself,
expect Moore's Law to hold for at least another two decades.
Mosaic
Last modified: Sunday, September 01, 1996
An application that simplifies accessing documents on the World Wide Web. Originally
produced by the National Center for Supercomputing Applications (NCSA), Mosaic has
always been distributed as freeware. In 1994, however, the NCSA turned over
commercial development of the program to a company called Spyglass. There are now
several varieties of Mosaic, some free and some for sale.
Mozilla
Last modified: Monday, January 13, 2003
The original name for Netscape's browser, now called Navigator. Some people claim
that the term is a contraction of Mosaic Godzilla (e.g., Mosaic killer), since Mosaic was
the number one Web browser at the time Netscape began developing its product. The
term Mozilla is still used by many Web developers and appears in server log files that
identify the browsers being used.
In 1998, Netscape decided to make the source code for Navigator freely available to the
public, or open source. The Netscape group responsible for releasing the code is called
mozilla.org, and its Web site is www.mozilla.org.
MPEG
Last modified: Thursday, January 22, 2004
Short for Moving Picture Experts Group, and pronounced m-peg, a working group of ISO.
The term also refers to the family of digital video compression standards and file
formats developed by the group. MPEG generally produces better-quality video than
competing formats, such as Video for Windows, Indeo and QuickTime. MPEG files can
be decoded by special hardware or by software.
MPEG achieves high compression rate by storing only the changes from one frame to
another, instead of each entire frame. The video information is then encoded using a
technique called DCT. MPEG uses a type of lossy compression, since some data is
removed. But the diminishment of data is generally imperceptible to the human eye.
There are three major MPEG standards: MPEG-1, MPEG-2 and MPEG-4.
*
The most common implementations of the MPEG-1 standard provide a video
resolution of 352-by-240 at 30 frames per second (fps). This produces video quality
slightly below the quality of conventional VCR videos.
*
MPEG-2 offers resolutions of 720x480 and 1280x720 at 60 fps, with full CDquality audio. This is sufficient for all the major TV standards, including NTSC, and
even HDTV. MPEG-2 is used by DVD-ROMs. MPEG-2 can compress a 2 hour video
into a few gigabytes. While decompressing an MPEG-2 data stream requires only
modest computing power, encoding video in MPEG-2 format requires significantly
more processing power.
*
MPEG-4 is a graphics and video compression algorithm standard that is based
on MPEG-1 and MPEG-2 and Apple QuickTime technology. Wavelet-based MPEG-4
files are smaller than JPEG or QuickTime files, so they are designed to transmit video
and images over a narrower bandwidth and can mix video with text, graphics and 2-D
and 3-D animation layers. MPEG-4 was standardized in October 1998 in the ISO/IEC
document 14496.
•E-mail this definition to a colleague•
MP3
Last modified: Monday, May 17, 2004
The name of the file extension and also the name of the type of file for MPEG, audio
layer 3. Layer 3 is one of three coding schemes (layer 1, layer 2 and layer 3) for the
compression of audio signals. Layer 3 uses perceptual audio coding and psychoacoustic
compression to remove all superfluous information (more specifically, the redundant
and irrelevant parts of a sound signal. The stuff the human ear doesn't hear anyway). It
also adds a MDCT (Modified Discrete Cosine Transform) that implements a filter bank,
increasing the frequency resolution 18 times higher than that of layer 2.
The result in real terms is layer 3 shrinks the original sound data from a CD (with a bit
rate of 1411.2 kilobits per one second of stereo music) by a factor of 12 (down to 112128kbps) without sacrificing sound quality.
Because MP3 files are small, they can easily be transferred across the Internet.
NOC
Last modified: Thursday, October 18, 2001
Short for network operations center, the physical space from which a typically large
telecommunications network is managed, monitored and supervised. The NOC
coordinates network troubles, provides problem management and router configuration
services, manages network changes, allocates and manages domain names and IP
addresses, monitors routers, switches, hubs and UPS systems that keep the network
operating smoothly, manages the distribution and updating of software and
coordinates with affiliated networks. NOCs also provide network accessibility to users
connecting to the network from outside of the physical office space or campus.
OC
Last modified: Wednesday, August 18, 2004
Short for Optical Carrier, used to specify the speed of fiber optic networks conforming
to the SONET standard. The table shows the speeds for common OC levels.
OC = Speed
OC-1 = 51.85 Mbps
OC-3 = 155.52 Mbps
OC-12 = 622.08 Mbps
OC-24 = 1.244 Gbps
OC-48 = 2.488 Gbps
OC-192 = 9.952 Gbps
OC-255 = 13.21 Gbps
optical character recognition
Last modified: Thursday, December 19, 2002
Often abbreviated OCR, optical character recognition refers to the branch of computer
science that involves reading text from paper and translating the images into a form
that the computer can manipulate (for example, into ASCII codes). An OCR system
enables you to take a book or a magazine article, feed it directly into an electronic
computer file, and then edit the file using a word processor.
All OCR systems include an optical scanner for reading text, and sophisticated software
for analyzing images. Most OCR systems use a combination of hardware (specialized
circuit boards) and software to recognize characters, although some inexpensive
systems do it entirely through software. Advanced OCR systems can read text in large
variety of fonts, but they still have difficulty with handwritten text.
The potential of OCR systems is enormous because they enable users to harness the
power of computers to access printed documents. OCR is already being used widely in
the legal profession, where searches that once required hours or days can now be
accomplished in a few seconds.
OEM
Last modified: Monday, August 23, 2004
(pronounced as separate letters) Short for original equipment manufacturer, which is a
misleading term for a company that has a special relationship with computer
producers. OEMs buy computers in bulk and customize them for a particular
application. They then sell the customized computer under their own name. The term is
really a misnomer because OEMs are not the original manufacturers -- they are the
customizers.
Contrast with IHV.
object-oriented programming
Last modified: Tuesday, January 07, 2003
A type of programming in which programmers define not only the data type of a data
structure, but also the types of operations (functions) that can be applied to the data
structure. In this way, the data structure becomes an object that includes both data and
functions. In addition, programmers can create relationships between one object and
another. For example, objects can inherit characteristics from other objects.
One of the principal advantages of object-oriented programming techniques over
procedural programming techniques is that they enable programmers to create modules
that do not need to be changed when a new type of object is added. A programmer can
simply create a new object that inherits many of its features from existing objects. This
makes object-oriented programs easier to modify.
To perform object-oriented programming, one needs an object-oriented programming
language (OOPL). Java, C++ and Smalltalk are three of the more popular languages, and
there are also object-oriented versions of Pascal.
open source
Last modified: Friday, March 12, 2004
(1) Generically, open source refers to a program in which the source code is available to
the general public for use and/or modification from its original design free of charge,
i.e., open. Open source code is typically created as a collaborative effort in which
programmers improve upon the code and share the changes within the community.
Open source sprouted in the technological community as a response to proprietary
software owned by corporations.
(2) A certification standard issued by the Open Source Initiative (OSI) that indicates that
the source code of a computer program is made available free of charge to the general
public. The rationale for this movement is that a larger group of programmers not
concerned with proprietary ownership or financial gain will produce a more useful and
bug -free product for everyone to use. The concept relies on peer review to find and
eliminate bugs in the program code, a process which commercially developed and
packaged programs do not utilize. Programmers on the Internet read, redistribute and
modify the source code, forcing an expedient evolution of the product. The process of
eliminating bugs and improving the software happens at a much quicker rate than
through the traditional development channels of commercial software as the
information is shared throughout the open source community and does not originate
and channel through a corporation's research and development cogs.
OSI dictates that in order to be considered "OSI Certified" a product must meet the
following criteria:
*
The author or holder of the license of the source code cannot collect royalties on
the distribution of the program
*
The distributed program must make the source code accessible to the user
*
The author must allow modifications and derivations of the work under the
program's original name
*
No person, group or field of endeavor can be denied access to the program
*
The rights attached to the program must not depend on the program's being part
of a particular software distribution
*
The licensed software cannot place restrictions on other software that is
distributed with it.
opt-in e-mail
Last modified: Wednesday, May 19, 2004
A term that refers to promotional e-mails that have been requested by the individual
receiving them. Unlike spam promotional e-mails that get sent out to large lists of
recipients without regard to whether or not they want the information, opt-in e-mails
are only sent to people who specifically request them.
Opt-in e-mails are targeted and often personalized and carry information about specific
topics or promotions that users are interested in learning about. Typical opt-in e-mails
contain newsletters, product information or special promotional offers. For example, if a
user frequented a Web site that sold books and music online, that user could "opt in" to
receive announcements when his favorite author or musician released new material.
The promotional e-mail may even present the recipient with a special promotional offer
to purchase the product at a discount available only to those on the opt-in list.
Spammers, however, have found a way to use the opt-in feature to their advantage.
Spam e-mails often come with opt-in features in fine print or obscured somewhere in
the body of the e-mail with text that reads something to the effect of "Failure to respond
to this e-mail will automatically opt-in the recipient to future mailings." The strategy of
responding to the spam and asking to be removed from future mailings also has critics
as some claim that responding to a spam e-mail with a request to be removed from the
mailing list signals that the e-mail address is a working address and the address can
then be passed on to other spammers.
Oracle
Last modified: Friday, September 26, 2003
Based in Redwood, California, Oracle Corporation is the largest software company
whose primary business is database products. Historically, Oracle has targeted highend workstations and minicomputers as the server platforms to run its database
systems. Its relational database was the first to support the SQL language, which has
since become the industry standard.
Along with Sun Microsystems, Oracle has been one of the leading champions of
network computers.
packet
Last modified: Tuesday, August 03, 2004
(pak´it) (n.) A piece of a message transmitted over a packet-switching network. See
under packet switching. One of the key features of a packet is that it contains the
destination address in addition to the data. In IP networks, packets are often called
datagrams.
Perl
Last modified: Friday, March 12, 2004
Short for Practical Extraction and Report Language, Perl is a programming language
developed by Larry Wall, especially designed for processing text. Because of its strong
text processing abilities, Perl has become one of the most popular languages for writing
CGI scripts. Perl is an interpretive language, which makes it easy to build and test
simple programs.
PGP (yields)
Pretty Good Privacy
Last modified: Wednesday, May 19, 2004
(n.) Abbreviated as PGP, a technique developed by Philip Zimmerman for encrypting
messages. PGP is one of the most common ways to protect messages on the Internet
because it is effective, easy to use, and free. PGP is based on the public-key method,
which uses two keys -- one is a public key that you disseminate to anyone from whom
you want to receive a message. The other is a private key that you use to decrypt
messages that you receive.
To encrypt a message using PGP, you need the PGP encryption package, which is
available for free from a number of sources. The official repository is at the
Massachusetts Institute of Technology.
PGP is such an effective encryption tool that the U.S. government actually brought a
lawsuit against Zimmerman for putting it in the public domain and hence making it
available to enemies of the U.S. After a public outcry, the U.S. lawsuit was dropped, but
it is still illegal to use PGP in many other countries.
PING
Last modified: Tuesday, February 18, 2003
A utility to determine whether a specific IP address is accessible. It works by sending a
packet to the specified address and waiting for a reply. PING is used primarily to
troubleshoot Internet connections. There are many freeware and shareware Ping
utilities available for personal computers.
It is often believed that "Ping" is an abbreviation for Packet Internet Groper, but Ping's
author has stated that the names comes from the sound that a sonar makes.
pixel
Last modified: Wednesday, June 02, 2004
Short for Picture Element, a pixel is a single point in a graphic image. Graphics monitors
display pictures by dividing the display screen into thousands (or millions) of pixels,
arranged in rows and columns. The pixels are so close together that they appear
connected.
The number of bits used to represent each pixel determines how many colors or shades
of gray can be displayed. For example, in 8-bit color mode, the color monitor uses 8 bits
for each pixel, making it possible to display 2 to the 8th power (256) different colors or
shades of gray.
On color monitors, each pixel is actually composed of three dots -- a red, a blue, and a
green one. Ideally, the three dots should all converge at the same point, but all monitors
have some convergence error that can make color pixels appear fuzzy.
The quality of a display system largely depends on its resolution, how many pixels it
can display, and how many bits are used to represent each pixel. VGA systems display
640 by 480, or about 300,000 pixels. In contrast, SVGA systems display 800 by 600, or
480,000 pixels. True Color systems use 24 bits per pixel, allowing them to display more
than 16 million different colors.
POP
Last modified: Tuesday, May 13, 2003
(1) Short for Post Office Protocol, a protocol used to retrieve e-mail from a mail server.
Most e-mail applications (sometimes called an e-mail client) use the POP protocol,
although some can use the newer IMAP (Internet Message Access Protocol).
There are two versions of POP. The first, called POP2, became a standard in the mid80's and requires SMTP to send messages. The newer version, POP3, can be used with
or without SMTP.
(2) Short for point of presence, an access point to the Internet. ISPs have typically
multiple POPs. A point of presence is a physical location, either part of the facilities of a
telecommunications provider that the ISP rents or a separate location from the
telecommunications provider, that houses servers, routers, ATM switches and
digital/analog call aggregators.
queue
Last modified: Friday, February 13, 2004
(v.) To line up. In computer science, queuing refers to lining up jobs for a computer or
device. For example, if you want to print a number of documents, the operating system
(or a special print spooler) queues the documents by placing them in a special area
called a print buffer or print queue. The printer then pulls the documents off the queue
one at a time. Another term for this is print spooling .
The order in which a system executes jobs on a queue depends on the priority system
being used. Most commonly, jobs are executed in the same order that they were placed
on the queue, but in some schemes certain jobs are given higher priority.
(n.) (1) A group of jobs waiting to be executed.
(2) In programming, a queue is a data structure in which elements are removed in the
same order they were entered. This is often referred to as FIFO (first in, first out). In
contrast, a stack is a data structure in which elements are removed in the reverse order
from which they were entered. This is referred to as LIFO (last in, first out).
RAID
Last modified: Wednesday, July 28, 2004
(rÇd) Short for Redundant Array of Independent (or Inexpensive) Disks, a category of disk
drives that employ two or more drives in combination for fault tolerance and
performance. RAID disk drives are used frequently on servers but aren't generally
necessary for personal computers.
There are number of different RAID levels:
*
Level 0 -- Striped Disk Array without Fault Tolerance: Provides data striping
(spreading out blocks of each file across multiple disk drives) but no redundancy. This
improves performance but does not deliver fault tolerance. If one drive fails then all
data in the array is lost.
*
Level 1 -- Mirroring and Duplexing: Provides disk mirroring. Level 1 provides
twice the read transaction rate of single disks and the same write transaction rate as
single disks.
*
Level 2 -- Error-Correcting Coding: Not a typical implementation and rarely
used, Level 2 stripes data at the bit level rather than the block level.
*
Level 3 -- Bit-Interleaved Parity: Provides byte-level striping with a dedicated
parity disk. Level 3, which cannot service simultaneous multiple requests, also is rarely
used.
*
Level 4 -- Dedicated Parity Drive: A commonly used implementation of RAID,
Level 4 provides block-level striping (like Level 0) with a parity disk. If a data disk fails,
the parity data is used to create a replacement disk. A disadvantage to Level 4 is that
the parity disk can create write bottlenecks.
*
Level 5 -- Block Interleaved Distributed Parity: Provides data striping at the
byte level and also stripe error correction information. This results in excellent
performance and good fault tolerance. Level 5 is one of the most popular
implementations of RAID.
*
Level 6 -- Independent Data Disks with Double Parity: Provides block-level
striping with parity data distributed across all disks.
*
Level 0+1 – A Mirror of Stripes: Not one of the original RAID levels, two RAID 0
stripes are created, and a RAID 1 mirror is created over them. Used for both replicating
and sharing data among disks.
*
Level 10 – A Stripe of Mirrors: Not one of the original RAID levels, multiple
RAID 1 mirrors are created, and a RAID 0 stripe is created over these.
*
Level 7: A trademark of Storage Computer Corporation that adds caching to
Levels 3 or 4.
*
RAID S: EMC Corporation's proprietary striped pairty RAID system used in its
Symmetrix storage systems.
RAM
Last modified: Tuesday, February 24, 2004
Pronounced ramm, acronym for random access memory, a type of computer memory that
can be accessed randomly; that is, any byte of memory can be accessed without
touching the preceding bytes. RAM is the most common type of memory found in
computers and other devices, such as printers.
There are two basic types of RAM:
*
dynamic RAM (DRAM)
*
static RAM (SRAM)
The two types differ in the technology they use to hold data, dynamic RAM being the
more common type. Dynamic RAM needs to be refreshed thousands of times per
second. Static RAM does not need to be refreshed, which makes it faster; but it is also
more expensive than dynamic RAM. Both types of RAM are volatile, meaning that they
lose their contents when the power is turned off.
In common usage, the term RAM is synonymous with main memory, the memory
available to programs. For example, a computer with 8M RAM has approximately 8
million bytes of memory that programs can use. In contrast, ROM (read-only memory)
refers to special memory used to store programs that boot the computer and perform
diagnostics. Most personal computers have a small amount of ROM (a few thousand
bytes). In fact, both types of memory (ROM and RAM) allow random access. To be
precise, therefore, RAM should be referred to as read/write RAM and ROM as read-only
RAM.
reboot
Last modified: Monday, May 18, 1998
To restart a computer. In DOS, you can reboot by pressing the Alt, Control and Delete
keys simultaneously. This is called a warm boot. You can also perform a cold boot by
turning the computer off and then on again.
On Macs, you reboot by selecting the "Restart" option from the Special menu.
RFID
Last modified: Thursday, August 12, 2004
(pronounced as separate letters) Short for radio frequency identification, a technology
similar in theory to bar code identification. With RFID, the electromagnetic or
electrostatic coupling in the RF portion of the electromagnetic spectrum is used to
transmit signals. An RFID system consists of an antenna and a transceiver, which read
the radio frequency and transfer the information to a processing device, and a
transponder, or tag, which is an integrated circuit containing the RF circuitry and
information to be transmitted.
RFID systems can be used just about anywhere, from clothing tags to missiles to pet
tags to food -- anywhere that a unique identification system is needed. The tag can carry
information as simple as a pet owners name and address or the cleaning instruction on
a sweater to as complex as instructions on how to assemble a car. Some auto
manufacturers use RFID systems to move cars through an assembly line. At each
successive stage of production, the RFID tag tells the computers what the next step of
automated assembly is.
One of the key differences between RFID and bar code technology is RFID eliminates
the need for line-of-sight reading that bar coding depends on. Also, RFID scanning can
be done at greater distances than bar code scanning. High frequency RFID systems (850
MHz to 950 MHz and 2.4 GHz to 2.5 GHz) offer transmission ranges of more than 90
feet, although wavelengths in the 2.4 GHz range are absorbed by water (the human
body) and therefore has limitations.
RFID is also called dedicated short range communication (DSRC).
RGB monitor
Last modified: Tuesday, August 06, 2002
Short for red, green, blue monitor, a monitor that requires separate signals for each of the
three colors. This differs from color televisions, for example, which use composite video
signals, in which all the colors are mixed together. All color computer monitors are RGB
monitors.
An RGB monitor consists of a vacuum tube with three electron guns -- one each for red,
green, and blue -- at one end and the screen at the other end. The three electron guns
fire electrons at the screen, which contains a phosphorous coating. When the phosphors
are excited by the electron beams, they glow. Depending on which beam excites them,
they glow either red, green, or blue. Ideally, the three beams should converge for each
point on the screen so that each pixel is a combination of the three colors.
Also see The Science of Color and Northern vs. Southern Hemishpere Monitors in the
Did You Know . . . ? section of Webopedia.
RISC
Last modified: Tuesday, October 30, 2001
Pronounced risk, acronym for reduced instruction set computer, a type of microprocessor
that recognizes a relatively limited number of instructions. Until the mid-1980s, the
tendency among computer manufacturers was to build increasingly complex CPUs that
had ever-larger sets of instructions. At that time, however, a number of computer
manufacturers decided to reverse this trend by building CPUs capable of executing only
a very limited set of instructions. One advantage of reduced instruction set computers is
that they can execute their instructions very fast because the instructions are so simple.
Another, perhaps more important advantage, is that RISC chips require fewer
transistors, which makes them cheaper to design and produce. Since the emergence of
RISC computers, conventional computers have been referred to as CISCs (complex
instruction set computers).
There is still considerable controversy among experts about the ultimate value of RISC
architectures. Its proponents argue that RISC machines are both cheaper and faster, and
are therefore the machines of the future. Skeptics note that by making the hardware
simpler, RISC architectures put a greater burden on the software. They argue that this is
not worth the trouble because conventional microprocessors are becoming increasingly
fast and cheap anyway.
To some extent, the argument is becoming moot because CISC and RISC
implementations are becoming more and more alike. Many of today's RISC chips
support as many instructions as yesterday's CISC chips. And today's CISC chips use
many techniques formerly associated with RISC chips.
ROM
Last modified: Friday, February 08, 2002
Pronounced rahm, acronym for read-only memory, computer memory on which data has
been prerecorded. Once data has been written onto a ROM chip, it cannot be removed
and can only be read.
Unlike main memory (RAM), ROM retains its contents even when the computer is
turned off. ROM is referred to as being nonvolatile, whereas RAM is volatile.
Most personal computers contain a small amount of ROM that stores critical programs
such as the program that boots the computer. In addition, ROMs are used extensively in
calculators and peripheral devices such as laser printers, whose fonts are often stored in
ROMs.
A variation of a ROM is a PROM (programmable read-only memory). PROMs are
manufactured as blank chips on which data can be written with a special device called a
PROM programmer .
server
Last modified: Monday, July 26, 2004
(ser´ver) (n.) A computer or device on a network that manages network resources. For
example, a file server is a computer and storage device dedicated to storing files. Any
user on the network can store files on the server. A print server is a computer that
manages one or more printers, and a network server is a computer that manages network
traffic. A database server is a computer system that processes database queries.
Servers are often dedicated, meaning that they perform no other tasks besides their
server tasks. On multiprocessing operating systems, however, a single computer can
execute several programs at once. A server in this case could refer to the program that is
managing resources rather than the entire computer.
Also see the Server Types page in the Quick Reference section of Webopedia for a
comparison of server types.
client
Last modified: Tuesday, August 10, 2004
(kl¥´&nt) (n.) The client part of a client-server architecture. Typically, a client is an
application that runs on a personal computer or workstation and relies on a server to
perform some operations. For example, an e-mail client is an application that enables you
to send and receive e-mail.
SGML
Last modified: Tuesday, January 21, 2003
Short forStandard Generalized Markup Language, a system for organizing and tagging
elements of a document. SGML was developed and standardized by the International
Organization for Standards (ISO) in 1986. SGML itself does not specify any particular
formatting; rather, it specifies the rules for tagging elements. These tags can then be
interpreted to format elements in different ways.
SGML is used widely to manage large documents that are subject to frequent revisions
and need to be printed in different formats. Because it is a large and complex system, it
is not yet widely used on personal computers. However, the growth of Internet, and
especially the World Wide Web, is creating renewed interest in SGML because the
World Wide Web uses HTML, which is one way of defining and interpreting tags
according to SGML rules.
SOAP
Last modified: Wednesday, March 12, 2003
Short for Simple Object Access Protocol, a lightweight XML-based messaging protocol
used to encode the information in Web service request and response messages before
sending them over a network. SOAP messages are independent of any operating system
or protocol and may be transported using a variety of Internet protocols, including
SMTP, MIME, and HTTP.
spam
Last modified: Tuesday, July 20, 2004
Electronic junk mail or junk newsgroup postings. Some people define spam even more
generally as any unsolicited e-mail. However, if a long-lost brother finds your e-mail
address and sends you a message, this could hardly be called spam, even though it's
unsolicited. Real spam is generally e-mail advertising for some product sent to a
mailing list or newsgroup.
In addition to wasting people's time with unwanted e-mail, spam also eats up a lot of
network bandwidth. Consequently, there are many organizations, as well as
individuals, who have taken it upon themselves to fight spam with a variety of
techniques. But because the Internet is public, there is really little that can be done to
prevent spam, just as it is impossible to prevent junk mail. However, some online
services have instituted policies to prevent spammers from spamming their subscribers.
There is some debate about the source of the term, but the generally accepted version is
that it comes from the Monty Python song, "Spam spam spam spam, spam spam spam
spam, lovely spam, wonderful spam…" Like the song, spam is an endless repetition of
worthless text. Another school of thought maintains that it comes from the computer
group lab at the University of Southern California who gave it the name because it has
many of the same characteristics as the lunchmeat Spam:
*
Nobody wants it or ever asks for it.
*
No one ever eats it; it is the first item to be pushed to the side when eating the
entree.
*
Sometimes it is actually tasty, like 1% of junk mail that is really useful to some
people.
Also see spim.
Also see Getting Rid of Spam in the Did You Know section of Webopedia.
SQL
Last modified: Wednesday, March 10, 2004
Abbreviation of structured query language, and pronounced either see-kwell or as
separate letters. SQL is a standardized query language for requesting information from
a database. The original version called SEQUEL (structured English query language) was
designed by an IBM research center in 1974 and 1975. SQL was first introduced as a
commercial database system in 1979 by Oracle Corporation.
Historically, SQL has been the favorite query language for database management
systems running on minicomputers and mainframes. Increasingly, however, SQL is
being supported by PC database systems because it supports distributed databases
(databases that are spread out over several computer systems). This enables several
users on a local-area network to access the same database simultaneously.
Although there are different dialects of SQL, it is nevertheless the closest thing to a
standard query language that currently exists. In 1986, ANSI approved a rudimentary
version of SQL as the official standard, but most versions of SQL since then have
included many extensions to the ANSI standard. In 1991, ANSI updated the standard.
The new standard is known as SAG SQL.
sysop
Last modified: Sunday, September 01, 1996
Pronounced siss-op, short for system operator, an individual who manages a bulletin
board system (BBS) , online service , or special interest group (SIG).
T-1 carrier
Last modified: Wednesday, January 09, 2002
A dedicated phone connection supporting data rates of 1.544Mbits per second. A T-1
line actually consists of 24 individual channels, each of which supports 64Kbits per
second. Each 64Kbit/second channel can be configured to carry voice or data traffic.
Most telephone companies allow you to buy just some of these individual channels,
known as fractional T-1 access.
T-1 lines are a popular leased line option for businesses connecting to the Internet and
for Internet Service Providers (ISPs) connecting to the Internet backbone. The Internet
backbone itself consists of faster T-3 connections.
T-1 lines are sometimes referred to as DS1 lines.
table
Last modified: Tuesday, January 13, 2004
Refers to data arranged in rows and columns. A spreadsheet, for example, is a table. In
relational database management systems, all information is stored in the form of tables.
tag
Last modified: Tuesday, January 21, 2003
(n) A command inserted in a document that specifies how the document, or a portion
of the document, should be formatted. Tags are used by all format specifications that
store documents as text files. This includes SGML and HTML.
(v) To mark a section of a document with a formatting command.
TCP
Last modified: Monday, April 12, 2004
Abbreviation of Transmission Control Protocol, and pronounced as separate letters. TCP
is one of the main protocols in TCP/IP networks. Whereas the IP protocol deals only
with packets, TCP enables two hosts to establish a connection and exchange streams of
data. TCP guarantees delivery of data and also guarantees that packets will be delivered
in the same order in which they were sent.
telephony
Last modified: Friday, February 28, 2003
The science of translating sound into electrical signals, transmitting them, and then
converting them back to sound; that is, the science of telephones. The term is used
frequently to refer to computer hardware and software that performs functions
traditionally performed by telephone equipment. For example, telephony software can
combine with your modem to turn your computer into a sophisticated answering
service. Voice mail is another popular telephony application.
Telnet
Last modified: Monday, July 26, 2004
(tel´net) (n.) A terminal emulation program for TCP/IP networks such as the Internet.
The Telnet program runs on your computer and connects your PC to a server on the
network. You can then enter commands through the Telnet program and they will be
executed as if you were entering them directly on the server console. This enables you
to control the server and communicate with other servers on the network. To start a
Telnet session, you must log in to a server by entering a valid username and password.
Telnet is a common way to remotely control Web servers.
terabyte
Last modified: Friday, June 21, 2002
2 to the 40th power (1,099,511,627,776) bytes. This is approximately 1 trillion bytes.
petabyte
Last modified: Tuesday, March 12, 2002
2 to the 50th power (1,125,899,906,842,624) bytes. A petabyte is equal to 1,024 terabytes.
TIFF
Last modified: Tuesday, April 02, 2002
Acronym for tagged image file format, one of the most widely supported file formats for
storing bit-mapped images on personal computers (both PCs and Macintosh
computers). Other popular formats are BMP and PCX.
TIFF graphics can be any resolution, and they can be black and white, gray-scaled, or
color. Files in TIFF format often end with a .tif extension.
unique visitor
Last modified: Thursday, June 13, 2002
When tracking the amount of traffic on a Web site, it refers to a person who visits a
Web site more than once within a specified period of time. Software that tracks and
counts Web site traffic can distinguish between visitors who only visit the site once and
unique visitors who return to the site. Different from a site's hits or page views -- which
are measured by the number of files that are requested from a site -- unique visitors are
measured according to their unique IP addresses, which are like online fingerprints,
and unique visitors are counted only once no matter how many times they visit the site.
There are some ISPs that use Dynamic Host Configuration Protocol, such as AOL and
cable modem providers, which use different IPs for every file requested, making one
visitor look like many. In this case, a single IP address does not indicate a unique
visitor.
user session
Last modified: Wednesday, April 14, 2004
(1) The session of activity that a user with a unique IP address spends on a Web site
during a specified period of time. The number of user sessions on a site is used in
measuring the amount of traffic a Web site gets. The site administrator determines what
the time frame of a user session will be (e.g., 30 minutes). If the visitor comes back to the
site within that time period, it is still considered one user session because any number
of visits within that 30 minutes will only count as one session. If the visitor returns to
the site after the allotted time period has expired, say an hour from the initial visit, then
it is counted as a separate user session.
Contrast with unique visitor, hit, click-through and page view, which are all other ways
that site administrators measure the amount of traffic a Web site gets.
(2) The period of time a user interfaces with an application. The user session begins
when the user accesses the application and ends when the user quits the application.
UNIX
Last modified: Monday, September 22, 2003
Pronounced yoo-niks, a popular multi-user, multitasking operating system developed at
Bell Labs in the early 1970s. Created by just a handful of programmers, UNIX was
designed to be a small, flexible system used exclusively by programmers.
UNIX was one of the first operating systems to be written in a high-level programming
language, namely C. This meant that it could be installed on virtually any computer for
which a C compiler existed. This natural portability combined with its low price made it
a popular choice among universities. (It was inexpensive because antitrust regulations
prohibited Bell Labs from marketing it as a full-scale product.)
Bell Labs distributed the operating system in its source language form, so anyone who
obtained a copy could modify and customize it for his own purposes. By the end of the
1970s, dozens of different versions of UNIX were running at various sites.
After its breakup in 1982, AT&T began to market UNIX in earnest. It also began the
long and difficult process of defining a standard version of UNIX.
Due to its portability, flexibility, and power, UNIX has become a leading operating
system for workstations. Historically, it has been less popular in the personal computer
market.
Today, the trademarked "Unix" and the "Single UNIX Specification" interface are owned
by The Open Group. An operating system that is certified by The Open Group to use
the UNIX trademark conforms to the Single UNIX Specification.
According to The Open Group's Web site, "As the owner of the UNIX trademark, The
Open Group has separated the UNIX trademark from any actual code stream itself, thus
allowing multiple implementations. Since the introduction of the Single UNIX
Specification, there has been a single, open, consensus specification that defines the
requirements for a conformant UNIX system. There is also a mark, or brand, that is
used to identify those products that have been certified as conforming to the Single
UNIX Specification, initially UNIX 93, followed subsequently by UNIX 95, UNIX 98 and
now UNIX 03. Both the specification and the UNIX trade mark are managed and held in
trust for the industry by The Open Group."
URL
Last modified: Thursday, January 08, 2004
Abbreviation of Uniform Resource Locator, the global address of documents and other
resources on the World Wide Web.
The first part of the address indicates what protocol to use, and the second part specifies
the IP address or the domain name where the resource is located.
For example, the two URLs below point to two different files at the domain
pcwebopedia.com. The first specifies an executable file that should be fetched using the
FTP protocol; the second specifies a Web page that should be fetched using the HTTP
protocol:
*
*
ftp://www.pcwebopedia.com/stuff.exe
http://www.pcwebopedia.com/index.html
USB
Last modified: Wednesday, February 04, 2004
Short for Universal Serial Bus, an external bus standard that supports data transfer rates
of 12 Mbps. A single USB port can be used to connect up to 127 peripheral devices, such
as mice, modems, and keyboards. USB also supports Plug-and-Play installation and hot
plugging.
Starting in 1996, a few computer manufacturers started including USB support in their
new machines. It wasn't until the release of the best-selling iMac in 1998 that USB
became widespread. It is expected to completely replace serial and parallel ports.
Also see USB 2.0.
user session
(1) The session of activity that a user with a unique IP address spends on a Web site
during a specified period of time. The number of user sessions on a site is used in
measuring the amount of traffic a Web site gets. The site administrator determines what
the time frame of a user session will be (e.g., 30 minutes). If the visitor comes back to the
site within that time period, it is still considered one user session because any number
of visits within that 30 minutes will only count as one session. If the visitor returns to
the site after the allotted time period has expired, say an hour from the initial visit, then
it is counted as a separate user session.
Contrast with unique visitor, hit, click-through and page view, which are all other ways
that site administrators measure the amount of traffic a Web site gets.
(2) The period of time a user interfaces with an application. The user session begins
when the user accesses the application and ends when the user quits the application.
vaporware
Last modified: Tuesday, May 19, 1998
A sarcastic term used to designate software and hardware products that have been
announced and advertised but are not yet available.
vector graphics
Last modified: Sunday, September 01, 1996
Same as object-oriented graphics, refers to software and hardware that use geometrical
formulas to represent images. The other method for representing graphical images is
through bit maps, in which the image is composed of a pattern of dots. This is
sometimes called raster graphics. Programs that enable you to create and manipulate
vector graphics are called draw programs, whereas programs that manipulated bitmapped images are called paint programs.
Vector-oriented images are more flexible than bit maps because they can be resized and
stretched. In addition, images stored as vectors look better on devices (monitors and
printers) with higher resolution, whereas bit-mapped images always appear the same
regardless of a device's resolution. Another advantage of vector graphics is that
representations of images often require less memory than bit-mapped images do.
Almost all sophisticated graphics systems, including CADD systems and animation
software, use vector graphics. In addition, many printers (PostScript printers, for
example) use vector graphics. Fonts represented as vectors are called vector fonts, scalable
fonts, object-oriented fonts, and outline fonts.
Note that most output devices, including dot-matrix printers, laser printers, and display
monitors, are raster devices (plotters are the notable exception). This means that all
objects, even vector objects, must be translated into bit maps before being output. The
difference between vector graphics and raster graphics, therefore, is that vector graphics
are not translated into bit maps until the last possible moment, after all sizes and
resolutions have been specified. PostScript printers, for example, have a raster image
processor (RIP) that performs the translation within the printer. In their vector form,
therefore, graphics representations can potentially be output on any device, with any
resolution, and at any size.
W3C
Last modified: Thursday, October 31, 2002
Short for World Wide Web Consortium, an international consortium of companies
involved with the Internet and the Web. The W3C was founded in 1994 by Tim BernersLee, the original architect of the World Wide Web. The organization's purpose is to
develop open standards so that the Web evolves in a single direction rather than being
splintered among competing factions.
WAN
Last modified: Wednesday, March 26, 2003
Short for wide-area network.
WAP
Last modified: Friday, May 21, 2004
Short for the Wireless Application Protocol, a secure specification that allows users to
access information instantly via handheld wireless devices such as mobile phones,
pagers, two-way radios, smartphones and communicators.
WAP supports most wireless networks. These include CDPD, CDMA, GSM, PDC, PHS,
TDMA, FLEX, ReFLEX, iDEN, TETRA, DECT, DataTAC, and Mobitex.
WAP is supported by all operating systems. Ones specifically engineered for handheld
devices include PalmOS, EPOC, Windows CE, FLEXOS, OS/9, and JavaOS.
WAPs that use displays and access the Internet run what are called microbrowsers-browsers with small file sizes that can accommodate the low memory constraints of
handheld devices and the low-bandwidth constraints of a wireless-handheld network.
Although WAP supports HTML and XML, the WML language (an XML application) is
specifically devised for small screens and one-hand navigation without a keyboard.
WML is scalable from two-line text displays up through graphic screens found on items
such as smart phones and communicators. WAP also supports WMLScript. It is similar
to JavaScript, but makes minimal demands on memory and CPU power because it does
not contain many of the unnecessary functions found in other scripting languages.
Because WAP is fairly new, it is not a formal standard yet. It is still an initiative that was
started by Unwired Planet, Motorola, Nokia, and Ericsson.
Wi-Fi
Last modified: Friday, January 16, 2004
Short for wireless fidelity and is meant to be used generically when referring of any type
of 802.11 network, whether 802.11b, 802.11a, dual-band, etc. The term is promulgated
by the Wi-Fi Alliance.
Any products tested and approved as "Wi-Fi Certified" (a registered trademark) by the
Wi-Fi Alliance are certified as interoperable with each other, even if they are from
different manufacturers. A user with a "Wi-Fi Certified" product can use any brand of
access point with any other brand of client hardware that also is certified. Typically,
however, any Wi-Fi product using the same radio frequency (for example, 2.4GHz for
802.11b or 11g, 5GHz for 802.11a) will work with any other, even if not "Wi-Fi
Certified."
Formerly, the term "Wi-Fi" was used only in place of the 2.4GHz 802.11b standard, in
the same way that "Ethernet" is used in place of IEEE 802.3. The Alliance expanded the
generic use of the term in an attempt to stop confusion about wireless LAN
interoperability.
Also see the Wireless LAN Standards chart in the Quick Reference section of
Webopedia.
wiki
Last modified: Monday, May 19, 2003
(n.) A collaborative Web site comprised of the perpetual collective work of many
authors. Similar to a blog in structure and logic, a wiki allows anyone to edit, delete or
modify content that has been placed on the Web site using a browser interface,
including the work of previous authors. In contrast, a blog, typically authored by an
individual, does not allow visitors to change the original posted material, only add
comments to the original content.
The term wiki refers to either the Web site or the software used to create the site.
Wiki wiki means “quick” in Hawaiian. The first wiki was created by Ward Cunnigham
in 1995.
worm
Last modified: Thursday, April 22, 2004
(1) A program or algorithm that replicates itself over a computer network and usually
performs malicious actions, such as using up the computer's resources and possibly
shutting the system down. Also see virus.
(2) When used in all capital letters, WORM is an acronym for for write once, read many,
an optical disk technology that allows you to write data onto a disk just once. After that,
the data is permanent and can be read any number of times.
Unlike CD-ROMs, there is no single standard for WORM disks, which means that they
can only be read by the same type of drive that wrote them. This has hampered their
acceptance, although they have found a niche market as an archival media.
WORM is also called CD-R.
Also see Understanding CD Burner Speeds in the Did You Know . . . ? section of
Webopedia
World Wide Web
Last modified: Friday, January 09, 2004
A system of Internet servers that support specially formatted documents. The
documents are formatted in a markup language called HTML (HyperText Markup
Language) that supports links to other documents, as well as graphics, audio, and video
files. This means you can jump from one document to another simply by clicking on hot
spots. Not all Internet servers are part of the World Wide Web.
There are several applications called Web browsers that make it easy to access the
World Wide Web; Two of the most popular being Netscape Navigator and Microsoft's
Internet Explorer.
World Wide Web is not synonymous with the Internet.
Also see The Difference Between the Internet and the World Wide Web in the Did You
Know . . . ? section of Webopedia.
XML
Last modified: Tuesday, May 18, 2004
Short for Extensible Markup Language, a specification developed by the W3C. XML is a
pared-down version of SGML, designed especially for Web documents. It allows
designers to create their own customized tags, enabling the definition, transmission,
validation, and interpretation of data between applications and between organizations.
XSL
Last modified: Tuesday, January 21, 2003
Short for Extensible Style Language, a specification for separating style from content
when creating HTML or XML pages. The specifications work much like templates,
allowing designers to apply single style documents to multiple pages. XSL is the second
style specification to be offered by the World Wide Web Consortium (W3C
)(www.w3c.org). The first, called Cascading Style Sheets (CSS), is similar to XSL but
does not include two major XSL's innovations -- allowing developers to dictate the way
Web pages are printed, and specifications allowing one to transfer XML documents
across different applications. W3C released the first draft of XSL in August 1998, and
promotes the specifications as helpful to the Web's speed, accessibility, and
maintenance.
XSLT
Last modified: Tuesday, January 21, 2003
Short for Extensible Style Language Transformation, the language used in XSL style sheets
to transform XML documents into other XML documents.
An XSL processor reads the XML document and follows the instructions in the XSL
style sheet, then it outputs a new XML document or XML-document fragment.
This is extremely useful in e-commerce, where the same data need to be converted into
different representations of XML. Not all companies use the exact same programs,
applications and computer systems.
XSLT Recommendation was written and developed by the XSL Working Group and
became ratified by the W3C on November 16, 1999.
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