Module 3Module 3

Introduction To Computer System :

Structure & Processes

Introduction To Computer System :

Structure & Processes

Module ObjectivesModule Objectives

• At the end of the module, students should be able to: – understand the concept and functions of a computer

system– identify the component of a computer– identify the components of the central processing unit

and explain how they work together and interact with memory

– describe how program instructions are executed by the computer

– explain how data is represented in the computer– understand the concept of bit and byte– identify the types of ports and connectors

What is A Computer System ?What is A Computer System ?

• A functional unit, consisting of one or more computers and associated software, that uses common storage for the execution of the program.

• Consists of three components– People

• Computer programmer• Users/End-user

– Software– Hardware

Functions Of A Computer SystemFunctions Of A Computer System

Components Of A ComputerComponents Of A Computer

SystemsInterconnection

i.e. bus

CPU

MainMemory

Input / Output

Communication Lines

PeripheralsComputer

• Complex set of electronic circuitry

• Executes stored program instructions

• Two parts– Control unit– Arithmetic/logic

unit (ALU)

Central Processing UnitCentral Processing Unit

Sends data to

the CPU

Registers

Control Unit

ALUUnit

Processing

InputOutput

Secondary storage

Stores data and programs

Makes processed

info available

Central Processing Unit

Control UnitControl Unit

• Directs the computer system to execute stored program instructions

• Must communicate with memory and ALU

• Sends data and instructions from secondary storage to memory as needed

Arithmetic Logic UnitArithmetic Logic Unit

• Executes all arithmetic and logical operations• Arithmetic operations

– Addition, subtraction, multiplication, division

• Logical operations– Compare numbers, letters, or special characters– Tests for one of three conditions

• Equal-to condition• Less-than condition• Greater-than condition

Intel Advanced Micro Devices (AMD)

Cyrix Motorola (Apple)

Pentium IVPentium MMX

Pentium III

Popular CPUsPopular CPUs

• shared communication link• set of wires used to connect multiple subsystems• A Bus is also a fundamental tool for composing

large, complex systems• The input/output bus provides a pathway so that the

microprocessor can communicate with input/output devices

Systems Interconnection (Bus)Systems Interconnection (Bus)

Control

Data path

Mem

ory

ProcessorInput

Output

Input / Output BusInput / Output Bus

• An input/output bus contains expansion slots which hold expansion cards– ISA (Industry Standard Architecture) slot phased

out– PCI (Peripheral Component Interconnect) slots– AGP (Accelerated Graphics Port) slot usually for

graphics card– USB (Universal Serial Bus) – PCI Express (PCI-E) latest tech.

PCI slots

Expansion CardAGP slots PCI-E slots

Data Storage and the CPUData Storage and the CPU

• Two types of storage:– Primary storage (memory)

• Stores data temporarily / volatile• CPU refers to it for both program

instructions and data• Holds input to be processed or

holds results of processing

– Secondary storage• Long-term storage / non-volatile• Stored on external medium, such

as a disk

The CPU and MemoryThe CPU and Memory

• CPU cannot process data from disk or input device– It must first reside in memory

– Control unit retrieves data from disk and moves it into memory

• Items sent to ALU for processing– Control unit sends items to ALU, then sends back to

memory after processing

• Data and instructions held in memory until sent to an output or storage device or program is shut down

Temporary Storage AreasTemporary Storage Areas

• High-speed temporary storage areas– located within the CPU

• Work under direction of control unit– Accept, hold, and transfer

instructions or data– Keep track of where the

next instruction to be executed or needed data is stored

• Also known as primary storage / main memory– Often expressed as random-

access memory (RAM)– Not part of the CPU

• Holds data and instructions for processing

• Stores information only as long as the program is in operation

MemoryRegisters

The Machine CycleThe Machine Cycle

• The time required to retrieve, execute, and store an operation

• Components– Instruction time– Execution time

• System clock synchronizes operations

The Machine CycleThe Machine Cycle

• Instruction Time = I-Time– Fetch – Gets the next program instruction from the

computer’s memory– Decode – Figures out what the program is telling the

computer to do

• Execution Time = E-Time– Execute – Performs the requested action– Write-back (Store) – Writes (stores) the results to a

register or to memory

OFFON

0 1

OR = 1 bit

1

0

0 0 001 1

0 0 0 01 1

OR

= 1 Byte

= 1 Byte

OFF

0

0

How Computers Represent DataHow Computers Represent Data

• Bit (Binary digit) – On or off state of electric current; considered the basic unit of information; represented by 1s and 0s (binary numbers)

• Byte – Eight bits grouped together to represent a character (an alphabetical letter, a number, or a punctuation symbol); 256 different combinations

ON

1000 bits = 1 kilobit (kb)

1,000,000 bits = 1 megabit (mb)

1,000,000,000 bits = 1 gigabit (gb)

Kilobits per second (Kbps), Megabits per second (Mbps), and Gigabits per second (Gbps) are terms that describe units of data used in measuring data transfer rates – Example: 56 Kbps modem

BitsBits

BytesBytes

8 bits = 1 Byte

1024 Bytes = 1 Kilobyte (KB)

1,048,576 Bytes = 1 Megabyte (MB)

1,043,741,824 Bytes = 1 Gigabyte (GB)

1,099,511,627,776 Bytes = 1 Terabyte (TB)

• Kilobyte, megabyte, gigabyte, and terabyte are terms that describe large units of data used in measuring data storage –Example: 20 GB hard drive

• Each byte has 256 (28) possible values

• Kilobyte: 1024 (210) bytes– Memory capacity of older personal computers

• Megabyte: roughly one million (220) bytes– Personal computer memory – Portable storage devices (diskette, CD-ROM)

• Gigabyte: roughly one billion (230) bytes– Storage devices (hard drives)– Mainframe and network server memory

• Terabyte: roughly one trillion (240) bytes– Storage devices on very large systems

Storage SizesStorage Sizes

Coding SchemesCoding Schemes

• Provide a common way of representing a character of data

• Needed so computers can exchange data

• Common Schemes– ASCII– EBCDIC– Unicode

0 10 0 001 1= 4

= 4

Representing Characters : Character CodesRepresenting Characters : Character Codes

Character codes translate numerical data into characters readable by humans– American Standard Code for Information Interchange

(ASCII) – Eight bits equals one character; used by minicomputers and personal computers

– Extended Binary Coded Decimal Interchange Code (EBCDIC) – Eight bits equals one character; used by mainframe computers

– Unicode – Sixteen bits equals one character; over 65,000 combinations; used for foreign language symbols

ASCII

0 001 11 1 1

EBCDIC

Inside the System Unit / CasingInside the System Unit / Casing

Motherboard (mainboard) – Large printed circuit board with thousands of electrical circuits

Power supply – Transforms alternating current (AC) from wall outlets to direct current (DC) needed by the computer

Cooling fan – Keeps the system unit cool

Internal Speaker – Used for beeps when errors are encountered

Drive bays – Housing for the computer’s hard drive, floppy drive, and CD-ROM / DVD-ROM drives

Drive bays

On/off switch

Reset button

Indicator lights

FRONT

BACK

The front panel contains drive bays, various buttons, and indicator lights

Connectors and ports are physical receptacles located on the back to connect peripheral devices to the computer

Outside the System UnitOutside the System Unit

Types of Connectors / PortsTypes of Connectors / Ports

A 15 pin connector used for monitors

For graphics-intensive interaction

Data flows through eight wires allowing the transfer of eight bits of data

simultaneously; faster than serial ports

Allows up to 127 devices

to be connected at

a time.

keyboard port - Special

serial port to connect keyboard.

Mouse port – Special

serial port to connect

mouse.

Also called jacks, sound card connectors

accept stereo mini-plugs. Microphone, line-in, line-out, and speaker connectors are plugged into the

card.

Serial port – Data flows in a series of pulses, one after another one bit at a time; slow data

transfer rate.

Other Types of ConnectorsOther Types of Connectors

• Small computer system interface (SCSI) port – A parallel interface that enables up to eight devices to be connected to it

• 1394 (FireWire) port – A high-speed connection for up to 63 devices

• Infrared Data Association (IrDa) port – Infrared signals are used to communicate between peripheral devices and the system unit