1 ENG224 INFORMATION TECHNOLOGY – Part I 1. Introduction to Computers

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ENG224 INFORMATION TECHNOLOGY – Part I1. Introduction to Computers

1. 1. Introduction to ComputersIntroduction to Computers

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Reference

Peter Norton, Introduction to Computers, McGraw Hill, 5th Ed, 2003


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ENIAC • The first practical

computer• Built in 1945,

weighed more than 30 tons

• Require 1500 sq. feet

In 1949, Popular Mechanics magazine predicted “computers in the future may perhaps only weigh 1.5 tons !!!”


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Components of a computer system


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Hardware


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Hardware

CPU: Central Processing Unit– Brain of the computer– Manages all devices and performs the actual

processing of data– Carry out instructions given by user– For Personal Computer (PC), the CPU is usually

included in a single Integrated Circuit (IC) chip (called Microprocessor)

– Nowadays, one or more microprocessors (chips) can be used to form a CPU Parallel Processing


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Hardware Input and Output devices

– Interface between the outside world and the computer system

– Input devices: keyboard, mouse – Output devices: monitors, printers– Other I/O devices: network adapter, USB, disk

interface …


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Hardware Memory

– Internal memory / Main memoryRandom Access memory (RAM)

– Main feature 1: volatile requires continuous supply of electrical power to retain information

– Main feature 2: cheap in terms of bytes per dollar suitable for large volume data storage

– Functions: Receive commands / data from keyboard Store info ready to be sent to output Store currently running programs/their data Store immediate data generated by the currently running programs


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Another kind of memoryRead Only Memory (ROM)

– Main feature 1: non-volatile data retain even when the power is off

– Main feature 2: relatively expensive and can only be written once suitable for storing essential data but in small volume

– Usually used for system boot up and basic control of I/O devices When a computer first powers up, nothing is in RAM Need ROM to store the instructions to set up various I/O devices, such as disk interface card, video adapter card, sound card, etc.

– ROM is used to store BIOS (Basic Input/Output Systems)

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Hardware

Storage devices– External memory

Non-volatile Used to store programs/data for future use Also used when the capacity of the internal storage is

insufficient to keep the currently running programs and the data required

Floppy disks, hard disks, CD ROMs, Magnetic tapes


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Hardware

Main differences between storage & memory:– Larger capacity in storage than in memory– Data in storage are retained while data in memory

disappear when power is off– Storage is much cheaper than memory


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Stored Program Concept – In 1949, Dr John Von Neumann defined the stored

program concept that greatly affected the development of nowadays computers

– Suggested that program instructions should be stored in a memory unit just like data

Instructions: Commands of user Data: Information that commands work on

– Hence rather than hardware programmable, should be software programmable

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User interacts with application software System software enables the application software

to interact with computer CPU and help the computer to manage its internal resources (hardware)

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Application Software

Develop to fulfill certain needs of users Either customized or packaged

– Customized software Designed for a particular customer according to their

needs Payroll, inventory control, …

– Packaged software Developed for general use Microsoft word, excel, Access, power-point, …


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System Software

Exists primarily for the computer itself Hides the hardware complexities Brings the different hardware configurations

into common platforms and accessible by the users

Consists of several programs, the most important one is the operating system (master control program that runs the computer)


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Operating System Master control program

– Manage all resources of the computer CPU, memory, disk, monitor, network, …

– Co-ordinate running programs Runs as soon as the computer boots

up, until the computer shuts down Usually store in the hard disk and load

into the memory when the computer starts

Need the help of BIOS for I/O devices E.g. Windows, Unix, Linux


BIOS

Operating System

I/O DevicesOther resources

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• When power up, nothing is in RAM. No control is possible to the hard disk to load the OS

• CPU starts to read the BIOS instructions stored in the ROM

• Things that normally perform– Initialize all I/O devices: hard disk, video, mouse,

keyboard, CD-ROM, etc– Load the bootstrap loader of the operating system

to RAM– Start to execute the bootstrap loader in RAM

• The bootstrap loader further loads the other part of the operating system to the RAM


How the OS is loaded into memory?

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CPU

Main Memory (RAM)

BIOS(Stored in

ROM)

Hard Disk

Mother Board

Disk Interface

Video Interface

Monitor

Disk Interface

Video Interface

Bootstrap loader

Bootstrap loader

OS

OS


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1 ENG224 INFORMATION TECHNOLOGY – Part I 1. Introduction to Computers