Terms 7
Definitions and Questions
File Formats
Files of the same type tend to have the
same extension – a 1-3 character code
after a period.
While sometimes these files are stored in
similar formats, often files of a given
extension will have completely different
formats.
Today we’ll be talking about 17 common
file formats
File Extension Dangers
On may versions of Windows and the
Mac OS, the ability to see File extensions
is turned off by default
This is dangerous since a malicious file
can have more than one extension
Think about “virus.exe.jpg” – how will your
computer display this file?
You can always turn file extensions on
Image File Formats
JPEG/JPG
(Joint Photographic Experts Group)
A standardized image compression
mechanism designed for compressing
either full-color or grayscale photographic
images, often for use on the Web.
JPG is "lossy," meaning that the
decompressed image is not quite of the
same quality as the original image.
GIF
(Graphic Interchange Format)
This format was developed by
CompuServe and has become an
Internet standard for exchanging
files across multiple platforms.
All graphical Web browsers will
load and place valid GIF files.
BMP
(bitmap)
The standard graphics file format
on Windows-compatible
computers.
Bitmap graphics support 24-bit
color
PNG
(Portable Network Graphics)
This format compresses the file with a
different algorithm than with GIF format.
Sample depths range from 1 to 16 bits.
PNG is robust, providing both full file
integrity checking and simple detection of
common transmission errors
Picture formats
Q: Which of these formats supports animated
pictures, like this one?
A: GIF. JPG/BMP do not
at all, and PNG has a
“cousin” called MNG that
does.
Audio File Formats
MP3
(MPEG-1/2 Audio Layer 3) is a standard
technology and format for compressing a sound
sequence into a very small file (about 1/12th the
size of the original file) while preserving the
original level of sound quality when it is played.
The mp3 format reduces data about sound that
most listeners can not perceive. Mp3s are bigger
files than .wma and .ogg file extensions. Most
audio applications support MP3 files.
WMA
WMA is the Windows Media Audio format
for digital music, launched by Microsoft as
an alternative to the MP3 format.
WMA files can be encoded to restrict
playback to a certain number of plays,
time periods or use by a single PC. Wma
files can also be streamed. These files
sound worse than mp3s but are smaller
files.
OGG
Ogg (Ogg Vorbis) is an audio file
extension. It is the same quality as an
mp3.
The size of the file is much smaller than an
mp3 and about the size of a wma. You
can play these ogg files on the newest
versions of Winamp and other players.
WAV
Wav stands for Waveform. It is a high quality
audio format that is not compressed.
Since they can not be compressed they are
always large files (about 10 Megs a minute).
Wav files have lost popularity over the past few
years due to file sharing on the internet. People
would rather transfer or download smaller files.
Video File Formats
AVI
AVI (Audio Video Interleaved) file is a
sound and motion picture file that
conforms to the Microsoft Windows
Resource Interchange File Format (RIFF)
specification.
AVI files tend to be much larger than
equivalent MPG files, and end with an .avi
extension.
RM / MOV
RM (Real Media) file is a streaming media
file format that plays in Real Media
Players, such as Real Player & RealOne
Player.
MOV (QuickTime Movie) files are a
streaming file format that plays with
Quicktime Player. QuickTime originated on
the Mac, but has made the transition to the
PC and is hugely popular.
MPEG
MPEG (pronounced EHM-pehg), the Moving
Picture Experts Group developed this standard
for digital video and digital audio compression. It
operates under the auspices of the International
Organization for Standardization (ISO). The
MPEG standards are an evolving series, each
designed for a different purpose.
(Note that .mp3 file suffixes indicate MP3
(MPEG-1 audio layer-3) files, not MPEG-3
standard files.)
System File Formats (executable)
Batch File / BAT
In DOS and Windows, a batch file is a text file with a series of commands
intended to be executed by the command interpreter. When the batch file is
run, the shell program (usually command.com or cmd.exe) reads the file
and executes its commands.
A batch file is analogous to a shell script in Unix-like operating systems.
In DOS systems, batch files are often called BAT files because their
filenames end with a.BAT extension. Batch files are useful for storing sets of
commands that are always executed together because you can simply enter
the name of the batch file instead of entering each command individually.
Autoexec.bat stands for automatically executed batch file, the file that DOS
automatically executes when a computer boots up.
This is a convenient place to put commands you always want to execute at
the beginning of a computing session. For example, you can set system
parameters such as the date and time, and install memory-resident
programs.
COM file
In DOS environments, a COM file is an executable
command file with a .COM filename extension. COM
files can be directly executed and are usually slightly
smaller than equivalent EXE files. However, COM files
cannot exceed 64K, so large programs are usually
stored in EXE files
Internal commands are commands, such as COPY and
DIR, that can be handled by the COMMAND.COM
program.
EXE file
Executable (.exe)
A filename extension that indicates the file is an executable
program.
An exe file is a program for some version of MS-DOS or MSWindows. It will probably not work on a platform other than the one
for which it was designed (including the different variants of MSWindows).
Similar to, but usually larger than, a com file.
To run the program, the user need only type the filename (without
the EXE extension) at the command prompt and press Enter.
Can be dangerous (if you don’t absolutely trust the source of the file)
Executable file
A file in a format that the computer can directly
execute (run). Unlike source files, executable
files cannot be read by humans. To transform a
source file into an executable file, you
need to pass it through a compiler or assembler.
In DOS systems, executable files have either a
.COM or .EXE extension and are called
COM files and EXE files, respectively.
Executable Files
Q: Which type of file (BAT, COM, or EXE)
could you write yourself to perform small
tasks?
A: A batch file.
System File Formats
(configuration)
SYS
Common file format that stores
system settings and variables for
DOS and Windows; was not made to
be regularly edited
They usually contain source information
and tell a computer how to perform a
particular task. An example would be
“config.sys”
INI
A text-based file format for depicting software configuration data in a
format which is easily editable by humans and unambiguously
readable by a simple automatic parser
INI is a file name extension used in Microsoft Windows. The letters stand for
initialization. As this term implies, INI files are used to initialize, or set
parameters for, the operating system and certain programs.
In Windows, two common INI files are SYSTEM.INI and WIN.INI. It is
possible to get some idea of what these files do by opening them in a plaintext (ASCII) word processor or in a DOS editor. The files contain statements
that set various parameters for the mouse, keyboard, peripherals, screen
colors, passwords, and so on. Under ordinary circumstances, no changes
should be made to these files in the text editor. (If the text editor presents
the option to "Save changes" upon closing, click on "No.")
In Windows 95, 98, NT, and later versions, much of the configuration is
done through values in the registry, rather than through INI files. Certain
programs contain their own INI files. The contents of these files are normally
modified by changing the characteristics of a program through the user
interface for that program, not by editing the files themselves.
DLL
Short for Dynamic Link Library, a library of executable
functions or data that can be used by a Windows
application.
This is a support file and is used by one or more
programs. For example, if several parts of a program
need to perform an action that action may be placed into
a .DLL file that the various program parts can all use.
This saves space and makes it easier when that
particular routine needs to be updated. Be careful, as
messing with a DLL file can seriously damage Windows
or programs if you do the wrong thing
A DLL can be used by several applications at the same
time. Some DLLs are provided with the Windows
operating system and available for any Windows
application. Other DLLs are written for a particular
application and are loaded with the application.
SYS, INI, DLL Q/A
Q: Which of these file formats frequently
contains hardware drivers?
A: DLL files are usually drivers.
Quiz
Please put away your notes, take out a
sheet of paper and write your name and
today’s date on it.
Quiz 3
1. Which of these ports is most comonly
used for mice and keyboards: Serial port,
PS2 port ?
2. __________ software is not protected by
copyright.
3. Define CPU.
4. T/F – USB is slower than Firewire.
Quiz 3
1. Which of these ports is most comonly
used for mice and keyboards: Serial port,
PS2 port ?
2. Public Domain software is not protected
by copyright.
3. Define CPU. – Central Processing Unit
4. T/F – USB is slower than Firewire.