Computer-based Information System
• Formal System
based on accepted and fixed definitions of data and procedures
(operating with predefined rules).
Formal system
manual
Computer-based
• Manual IS => use paper and pencil technology.
• Computer-bases IS => An information system that is based on
computer hardware and software technology for processing and
disseminating information.
Computer
• An electronic machine that accepts input,
processes data, stores data, and produces
output.
• Data can be numbers, text, images,
graphics, and sound, etc.
• Computer program is a set of instructions.
Without it computer is useless.
• Programming languages allow us to write
these instructions (e.g. C, C++, Java, etc).
Computer system
• A computer system consists of a computer, peripheral
devices, and software.
• The computer itself can take care of the processing
function, but it needs additional components, called
peripherals, to accomplish its input, output and storage
functions.
• Examples of peripheral devices are hard disk drive and
printer.
Computer Hardware
• Hardware is the physical component of a
computer.
• Hardware is the equipment used to perform
the necessary computations.
• Examples:
Main memory (RAM, ROM), secondary
memory (hard disk drive, floppy disk drive),
CPU, input devices (keyboard and mouse),
and output devices (monitor and printer).
Hardware Components of a Computer System
Central Processing Unit (CPU)
• Arithmetic-Logic Unit
• Control Unit
Input Devices
•
•
•
•
Secondary Storage
• Magnetic disk
• Optical disk
• Magnetic tape
Keyboard
Computer mouse
Touch screen
Source data automation
Output Devices
•
•
•
•
Printers
Video display terminals
Plotters
Audio output
Communications
Devices
Primary Storage
Main Memory
• Computer memory is a set of storage
locations on the main circuit board
(motherboard).
• Four types of memory:
– RAM, Virtual memory, ROM, and CMOS
(complementary metal oxide semiconductor
memory)
Random access memory
• Consists of electronic circuits on the
motherboard (main circuit board).
• Temporarily hold programs and data while
the computer is on.
• Each circuit has address that is used by the
microprocessor to transmit and store data.
• RAM is constantly changing (volatile).
• E.g. When we write a paper, the word
processing program will be temporarily
copied into RAM so that microprocessor
can quickly access the required instructions.
Virtual Memory
• Today’s microcomputer software uses space
on computer’s storage devices to simulate
RAM if more needed.
• This extra memory is called virtual memory.
• How it works?
• Suppose my computer is running a word
processing program that takes up most of
the memory in RAM, but I want to run a
spreadsheet program at the same time.
Virtual Memory (Cont.)
• The OS moves the infrequently used
segment of the word processing program
into virtual memory on disk.
• The spreadsheet program now can be
loaded into RAM.
• If that segment is later needed, it is copied
from virtual memory back to RAM.
• Disadvantage:It is much slower than RAM.
Read-only memory(ROM)
• Another set of electronic circuits on the
motherboard inside the computer.
• We cannot increase ROM capacity.
• Manufacturer permanently installs ROM.
• When computer is on, the sets of
instructions in ROM
– checks all the computer system’s components to
make sure they are working and
– activates the essential software that controls the
processing function.
Complementary metal oxide
semiconductor(CMOS)
• A chip installed on the motherboard.
• Activated during the boot process.
• Contains information about where the
essential software is stored.
• A small rechargeable battery powers CMOS.
• It changes every time we add or remove
hardware to the computer system.
• CMOS is referred as semipermanent memory.
Secondary Storage Devices
• RAM retains data only when the power is on, so
computer must have a more permanent storage option.
• Because secondary storage requires mechanical
movement to access the data, it is relatively slow.
• Information systems need to store information outside the
computer in a nonvolatile state and to store data too large
to fit into a computer of any size today (such as a large
payroll or U.S. census).
• The most common secondary storage: magnetic disk,
optical disk, and magnetic tape.
• Magnetic storage devices are hard disk drive, floppy disk
drives, and tape drives.
Hard disk drive
• Most computers contains one hard disk that
cannot be removed from drive.
• Provides a storage area to be shared by all
users of the computer.
• Generally, the programs that are needed to
operate the computer system are stored
here.
• Advantages over floppy disk: speed and
capacity.
Hard Disk Drive
Internal Components
Floppy disk drive
• Most common magnetic storage device.
• Users can have any number of floppy disks
that can be inserted into computer’s floppy
disk drive.
• High density disk- capacity to store 1.44
MB.
• Low-density disk - capacity to store 720
KB.
Tape drive
• Another magnetic storage device.
• Provides inexpensive archival storage for
large quantities of data.
• Too slow to be used for day-to-day tasks.
• Used to make backup copies of data stored
on hard disks.
• If a hard disk fails, data from the backup
tape can be reloaded on a new hard disk.
Compact Disk Read Only Memory (CD-ROM)
• Optical storage device.
• Uses laser technology to read and write data on
compact discs (CDs).
• High capacity and portability. Can store up to 660
MB, equivalent to about 400 floppy disks.
• Disadvantage: The surface of the CD is not
rewriteable like magnetic media. Once the laser
cuts a pit in its surface, the pit cannot be recut, so
the data stored there cannot be changed.
• Relatively slow access. Mainly used for software
distribution and storing large data files such as
graphics, animation, and video.
CD-RW
• One of the problems with a CD-R disk is that
information can only be written onto it once.
• A CD-RW disk (rewritable) allows the disk to be
written onto multiple times.
• Most new computers come with a CD-RW drive
so that users can store and backup large amounts
of information on a reusable disk.
Central Processing Unit (CPU)
• Coordinating all computer operations.
• Performs arithmetic and logical operations on data.
• To process a program stored in main memory,
- CPU retrieves each instruction in sequence.
-
Interprets the instruction to determine what should be
done.
- Retrieves any data needed to carry out that instruction
- Then CPU performs the actual manipulation.
• CPU’s current instruction and data values are stored
temporarily inside the CPU in special high-speed
memory locations called registers.
Central Processing Unit (CPU)
• The CPU consists of a control unit and an arithmetic-logic unit.
• The control unit coordinates and controls the other parts of the
computer system.
• The arithmetic-logic unit (ALU) performs the primary logical
and arithmetic operations of the computer.
• Three kind of buses link the CPU, primary storage, and other
devices in the computer systems.
• The data bus moves data to and from primary storage.
• The address bus transmits signals for locating a given address in
primary storage.
• The control bus transmits signals specifying whether to read or
write data to or from a given primary storage address, input
device, or output device.
Data Bus, Address Bus, and Control Bus
Central Processing Unit (CPU)
Primary Storage
1
Arithmetic-Logic Unit
24 + 12 = 36
12 < 24
8
#
T
U
Control Unit
Data Bus
Address Bus
Control Bus
Input Devices
Output Devices
Secondary
Storage
Machine Cycle
• The series of operations required to process a single
machine instruction is called the machine cycle.
• The machine cycle has two parts: instruction cycle and
execution cycle.
• During instruction cycle,
- the control unit retrieves one program instruction from
primary storage and decodes it.
- Places the part of the instruction telling the ALU what to do
next in a special instruction register and
- places the part of the specifying the address of the data to be
used in the operation into an address register.
Machine Cycle
• During the execution cycle,
-
the control unit locates the required data in primary
storage, places it in a storage register,
instructs the ALU to perform the desired operation,
temporary stores the result of the operation in an
accumulator, and
finally places the result in primary memory
• As the execution of each instruction is completed,
the control unit advances to and reads the next
instruction of the program
The Various steps in the Machine Cycle
3. Place into instruction
register
2. Decode instruction
1. Fetch instruction
Decoder
Instruction
register
Address
register
8. Send result to
accumulator
Storage
register
Accumulator
4.Place into address
register
5. Send data from
main memory to
storage register
CPU
7. ALU performs
desired operation
6. Command ALU to
perform desired operation
Input Devices
• Input device - keyboard, mouse.
• When we press a letter or digit key on a key
board, that character is sent to main
memory and displayed on the monitor.
• Keyboard consists of three major parts:
main keyboard, keypads, and function keys.
• A mouse is a hand-held device used to
select an operation.
Output Devices
• Shows the result of processing data.
• Output devices - monitor and printer.
• Monitor is the TV-like device that displays
the output from a computer.
• Printer produces a hard copy of the text or
graphics processed by the computer.
Processing Hardware
• The most important computer function is
processing data. To understand this you
need to learn how the computer represents
and stores data.
• Computer does not understand human
language because it is an electronic device
that interpret every signal as either “on” or
“off” like a light bulb.
Binary Representation of Data
• For information to flow through a computer system, it must be in
form suitable for processing.
• All symbols, pictures, or words must be reduced to a string of
binary digits.
• A binary digit is called a bit and it represents either a 0 or a 1.
• In the computer, the presence of an electronic or magnetic signal
means “one” and its absence means “zero”.
• A string of 8 bits that computer stores as a unit is called a byte.
• Each byte is used to store a decimal number, a symbol, a character,
or a part of a picture.
• By using binary number system a computer can express all
numbers as group of zeroes and ones.
• There are two standard binary codes:
EBCDIC (Extended Binary Coded Decimal Interchange Code)
ASCII (American Standard Code for Information Interchange).
Bits and Bytes
0
or
1
0 1 0 0 0 0 0 1
One bit
One byte for character A
The Computer representation in ASCII for the name ALICE is:
0 1 0 0 0 0 0 1
A
0 1 0 0 1 1 0 0
L
0 1 0 0 1 0 0 1
I
0 1 0 0 0 0 1 1
C
0 1 0 0 0 1 0 1
E
Data representation
• Computer represents “on” with a 1 and
“off” with a 0. These numbers are called
binary digits or bits.
• Binary number system: most widely used
method for interpreting bit settings as
nonnegative integers.
• 38 (decimal) = 21 +22+25 = 00100110
Ones complement notation
• One of the widely used methods for
representing negative binary numbers.
• A negative number is represented by
changing each bit to the opposite bit setting.
• Example:
• 38 (decimal) = 00100110 (binary)
• -38 (decimal) = 11011001 (binary)
Twos complement notation
• Another popular method of representing
negative binary number
• In this method, 1 is added to the ones
complement representation of a negative
number.
• Example:
-38 (decimal) = 11011001 (ones complement)
-38 (decimal) = 11011010 (twos complement)
Floating-point notation
• Usual method to represent real numbers
• Real number is represented by a number, called a
mantissa, times a base raised to an integer power,
called an exponent.
• Example:
387.53 = 38753 x 10 -2
Other possibilities .38753 x 10 3,
387.53 x100
(we choose mantissa is an integer with no tailing 0s)
Floating-point notation(cont.)
• A real number is represented by a 32-bit string.
• 24-bit for mantissa and 8-bit for exponent.
• Base is fixed to 10.
• Example
100 = 0000000000000000000000100000010
-387.53 = 11111111011010001001111111111110
387.53 = 00000000100101110110000111111110
( 24-bit binary representation of 38753 is
000000001001011101100001
8-bit twos complement binary representation of -2 is
11111110)
The Evolution of Computer Hardware
• There are four major stages, or computer generations, in
the evolution of computer hardware:
• Generations of Computer Hardware
- First Generation: Vacuum Tube technology, 1946-1956
- Second Generation: Transistors, 1957-1963
- Third Generation: Integrated Circuit, 1964-1979
- Fourth Generation: Very Large-Scale Integrated Circuits,
1980-1990
The Evolution of Computer Hardware
• First Generation: Vacuum Tube technology, 1946-1956
It is based on vacuum tubes to store and process information. These
tubes consumed a great deal of power, were short-lived, and
generated a great deal of heat.
Size: huge, limited memory (main memory 2 kilobytes), speed 10,
000 instructions per second.
• Second Generation: Transistors, 1957-1963
It is based on transistors to store and process information.
Transistors consumed less power, generate less heat.
However each transistor had to be individually made and wired into
a printed circuit board- sloe & tedious process.
Memory (32 kilobytes RAM), speed 200, 000- 300, 000 instructions
per second
The Evolution of Computer Hardware
• Third Generation: Integrated Circuits, 1964-1979
It is based on integrated circuits.
Integrated Circuits were made by printing hundred and later
thousands of tiny transistor s on small silicon chips. These devices
were called semiconductors.
Memory: 2 megabytes (RAM), speed: 5 MIPS.
• Fourth Generation: Very Large-Scale Integrated Circuits,
1980-Present
It is based on very large-scale integrated circuits (VLSIC).
VLSIC are packed with millions of circuits per chip.
Memory: over 2 gigabytes speed: 200 MIPS
Size: small.
Microprocessor
• VLSIC technology, with millions of transistors on a single chip,
integrates the computer’s memory, logic, and control on a single
chip => microprocessor, or computer on a chip.
• Computer speed depends on:
• Word length => no of bits that can be processed at one time by
the machine. The larger the word length, the greater the speed of
the computer. A 8-bit chip can process 8 bits of information in a
single machine cycle.
• Cycle speed => Every event in a computer must be sequenced so
that one step logically follows another. The control unit sets a beat
to the chip. It is measured in megahertz. 1 MHz = millions cycles
per second.
• Data bus width => Data bus acts as a high-way between the
CPU, primary storage, and other devices. Data bus width
determines how much data can be moved at one time.
Microprocessor
Computer speed depends on:
• Reduced instruction set computing (RISC) => Microprocessor
can be made faster by using RISC technology in its design.
- Some instructions that a computer uses to process data are
actually embedded in the chip circuitry.
- In the reduced instruction set computer, the only most
frequently used instructions are embedded in the chip
circuitry.
- A RISC CPU can execute most instructions in a single
machine cycle and sometimes multiple instructions at the
same time.
- RISC is very useful for scientific and workstation computing
where we perform repetitive operations.
Types of Computers: Microcomputers
• Computers are classified by their size, speed, and cost.
– Microcomputers
- desktop or tower.
- A notebook computer
- Personal digital assistant (PDA)
– Minicomputers
– Mainframes
– Supercomputers
Microcomputers
• Microcomputers => Also called personal computers.
• These computers are typically used by a single user,
usually at home or at office. They can be of different
shapes and sizes.
• A desktop or tower microcomputer costs between $500
and several thousand dollars.
• A notebook computer => small and light. Portable
(standard desktop does not have). It can run on power
from an electrical outlet or batteries. It costs between
$800 to several thousand dollars.
• Personal digital assistant (PDA) =>more portable than
notebook computer. We can surf the Web and perform
simple tasks. It costs between $200 and $500.
Workstations
• Workstations are a special class of
microcomputer designed for individual that
have the power of some minicomputers, but
they fit on a desktop.
• Computer hardware companies, such as
Silicon Graphics, Sun Microsystems, and
Hewlett-Packard are leaders for these
computers.
• Cost can be between $5,000 and $50,000
Minicomputers
• Minicomputers => Somewhat larger than
microcomputers. The computing capability
of a microcomputer may be more than a
minicomputer. Its cost can be between $20,
000 and $250, 000.
• Usually a company purchases a
minicomputer when it needs to share large
amount of data among many users.
• It can support from four to 200 users
simultaneously.
• It has become an integral to many smaller
and midsized organizations.
Mainframes
• Larger and powerful than minicomputers.
• The mainframe computers can handle many more users
than a minicomputer. It can support thousands of users
simultaneously.
• These are used to provide centralized storage,
processing, and management for large amounts of data.
• Its cost can be several million dollars.
• Large corporations, such as American Airlines, Holiday
Inn use mainframes to perform repetitive tasks.
Supercomputers
• The largest and fastest, most powerful, and most
expensive type of computer. It is based on parallel
processing.
• Its cost can be many million dollars.
• First developed for high volume computing tasks, such
as weather prediction.
• They are also used in a large corporation because they
can process tremendous volume of data in a relatively
shorter time compared to other computers.
(microcomputers, minicomputers, and mainframes).
• They have traditionally been used in scientific and
military work, but they are also starting to be used in
business.
Sequential and Parallel Processing
• Sequential Processing => each task is assigned to one CPU that
processes one instruction at a time.
• Parallel Processing => more than one instructions can be processed
at a time by breaking down problems into smaller parts and
processing them simultaneously with multiple processors.
Sequential Processing
Program
Task 1
CPU
Result
Program
CPU
Result
Parallel Processing
Program
task1
task2
CPU
CPU
task3
task4
CPU
Result
CPU
task5
CPU
Multimedia
• Multimedia technology integrates two or more types of
media, such as text, graphics, sound, voice, full-motion
video, still video, or animation into a computer-based
application.
• Multimedia is very useful in electronic books and
newspapers, electronic classroom presentation, full-motion
video conferencing, imaging, graphics design tools, and
video and voice mail.
• The most difficult element to incorporate into multimedia
information systems has been full-motion video, because
massive amount of data in video image must be digitally
encoded, stored, and manipulated electronically.(use
compression technique)
• The possibilities of this technology are endless.
Data Communications
• The transmission of text, numeric, voice, or video data
from one machine to another is called data
communications.
• For example, Send an electronic mail to your friends
around the globe.
• The four essential components of data communications
are a sender, a receiver, a channel, and a protocol.
Sender => The computer that originates the message is
called the sender.
Receiver => The computer at the message’s destination
is called the receiver.
Data Communications
Channel => The message needs some kind of medium
to be transmitted. This medium is called channel. For
example, telephone or coaxial cable, microwave signal,
or optical fibers
Protocol => The rules that establish an orderly transfer
of data between the sender and the receiver are called
protocols.
• Computer software and hardware establish these
protocols at the beginning of the transmission, and both
computers have to follow the protocols to ensure
accurate transfer of data.
Networks
• One of the most important types of data communications in
the business world is a network connection.
• A network connects one computer to another computers and
peripheral devices to share data and resources.
• There is a number of network configurations.
local area network (LAN) => computers and peripheral
devices are located relatively close to each other, generally
in the same building.
Client/server networks =>Some networks have file servers
(one or more computers) that act as the central storage
location for programs and that provide mass storage for
most of the data used on the network. A network with a file
server is called a client/server networks.
Networks
• Peer-to-peer networks => When a network does not
have a file server, all the computers essentially are
equal, and programs and data are distributed among
them. This is called a peer-to-peer network.
Each computer that is part of the network must have a
network interface card installed. This device creates a
communication channel between the computer and the
network.
Network software is also essential to establish the
communications protocols.
• Standalone computer => A microcomputer that is not
connected to a network is called a standalone computer.
Telecommunications
• Allows us to send and receive data over telephone
lines.
• A modem connects a computer to a telephone
jack.
• At the sending site, modem converts the digital
signal from a computer into analog (continuous
wave) signals (sound waves) that can traverse
ordinary phone lines (modulation).
• At the receiving site, a second modem converts
the analog signals back into digital signals
(demodulation).
Telecommunications
Internet
• The internet was originally developed for the government
to connect the researchers around the world to share data.
• Today, the internet is the largest network in the world that
connects millions of people in almost 200 countries.
• The use of internet:
electronic mail => This is the capability to send a message
from one user’s computer to another user’s computer
where it is stored until the receiver opens it. Message
passes through electronic links called gateways.
World Wide Web (Web) => Web is a huge database of
information that is stored on the network servers in places
that allow public access. The information is stored as text
files called web pages.
Internet
• Hyperlinks => a place on a computer screen that is
programmed to connect to a particular file on the same
network server, or on a network v=server on the other
side of the globe.
• Web browsing => communication software that help us
navigate the WWW is called web browsing software or
web browser.