Computer-based Information System• Formal System based on accepted and fixed definitions of data and procedures

(operating with predefined rules).

Formal system

• 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.

manual Computer-based

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

Input Devices

• Keyboard• Computer mouse• Touch screen• Source data automation

Central Processing Unit (CPU)• Arithmetic-Logic Unit• Control Unit

Primary Storage

Output Devices

• Printers• Video display terminals• Plotters• Audio output

Secondary Storage

• Magnetic disk• Optical disk• Magnetic tape

Communications Devices

Buses

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

Arithmetic-Logic Unit 24 + 12 = 36 12 < 24

Control Unit

Primary Storage

1

T

U

#

8

Input Devices Output DevicesSecondary

Storage

Central Processing Unit (CPU)

Data Bus

Address Bus

Control Bus

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

DecoderInstructionregister

Addressregister

Storageregister

Accumulator

CPU

6. Command ALU to perform desired operation

2. Decode instruction 3. Place into instructionregister

4.Place into address register

5. Send data from main memory to storage register

1. Fetch instruction

7. ALU performs desired operation

8. Send result toaccumulator

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 Bytes0 1or One bit

0 1 00 0 00 1 One byte for character A

The Computer representation in ASCII for the name ALICE is:

0 1 00 0 00 1

0 1 00 1 01 0

0 1 00 1 00 1

0 1 00 0 10 1

0 1 00 0 01 1

A

L

I

C

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.

Program

CPU

Program

CPU

Program

CPUCPUCPUCPU

Sequential Processing Parallel Processing

Result

Result

Result

Task 1

CPU

task1 task2 task3 task4 task5

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.