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Chapter 1

Introduction to computers

What is a Computer?

Computer is an electronic machine that can

receive, store or process data according to a

set of instructions (computer program) and

output information.

Processinput output

data information

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What is a computer?

Device consisting of: electronic components (hardware)

receives controlled instructions (software)

stored within its memory.

Components of a Computer System

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Categories of computers

Category Size

Personal computers

(desktops)

Be placed on a table

Mobile computers /

devices

Portable and fits by hand-carrying

Embedded computers Small and embedded into devices

Servers Small cupboard

Mainframes Half a room to a room full

Supercomputers A room full of equipments


Mainframes

Source: Google Images

Embedded computers

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Supercomputers


Data representation

Digital form

Two states: on and off Digit 0 = off

Digit 1 = on

Digit 0 and 1 is known as bits (short for binary

digit).

8 bits = a byte

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Binary coding scheme

Represents 256 different individual characters

Two most popular coding schemes:

American Standard Code for Information

Interchange (ASCII)

Extended Binary Coded Decimal Interchange Code

(EBCDIC)

Binary coding scheme

Symbol ASCII EBCDIC

A 0100 0001 1100 0001

B 0100 0010 1100 0010

1 0011 0001 1111 0001

2 0011 0010 1111 0010

# 0010 0011 0111 1011

& 0010 0110 0101 0000

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What happens?

ASCII to Binary conversion

01101010

jj

Input / Output Devices

Input is data or instructions that user or other

sources gives command to the computer on

how they should operate

Output is the useful outcome after the

computer has completed its operation

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Sample input

Sample output

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System Unit


System Unit

Contains all the electrical components that

the computer uses to process data.

Processor (central processing unit, CPU)

interprets and manages most of the

computers operation.


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Computer Hardware

Central Processing Unit (CPU)

2 roles of CPU coordinating all computer operations (control

unit), and

performing arithmetic and logical operations on

data (arithmetic and logic unit).

During the process, current instruction and

data are stored temporarily inside the CPUs

special high-speed memory locations called

registers.

Processor

Two parts:

control unit: directs and coordinate most

operations in the computer

arithmetic logic unit (ALU): performs arithmetic

and comparison.

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Memory

A temporary storage unit

3 things it stores:

Operating system and other system software of

the computer and its devices

Application programs with tasks

Data being processed by programs and its results.


Memory

2 kinds of memory - volatile (temporary) and

nonvolatile (permanent)

Volatile memory loses its contents when

power is turned off

Non-volatile memory does not lose its content

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Computer Hardware

Memory

Computer memory can be divided into twocategories

main memory secondary memory

There are 2 types of mainmemory

RAM temporary storageand volatile (contents isgone when the computer isswitch off)

ROM

stores informationpermanently and NOTvolatile

Provides semi-permanentdata storage capability

Memory

Transfer of data from storage to memory

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Memory

Each bytes resides temporarily in memory hasan address. This address is a unique number

that identifies the location of the memory.


Computer Hardware

Memory Memory an ordered

sequence of storagelocations or memorycells, each of which has aunique memory address

Memory cell anindividual storagelocation in memory

Assigning a new data toa memory cell willdestroy its previouscontent

1 byte == 8 bits

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Storage

Stores data, instructions and information to beused in the future

Eg. music, movies, assignment, pictures

Save data, instructions or information from

memory to storage medium, that process is

known as writing.

To recall data from a medium to memory, it is

known as reading.

Storage


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Computer Software

Instruction that instructs the computer whatto do and how to execute

There are Three (3) categories of computer

software

System Software

Application Software

Computer Languages

Software

System software - control and maintain the

operations of the computer and its devices.

Divided into 2:

operating system

utility programs


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Computer Software

Operating System

System Software = Operating System (OS)

softwarethat controls interaction of user and computerhardware and that manages allocation of computerresources. i. e. Communicating with the computer user

Collecting input from input devices.

Conveying program output to output devices

Managing allocation of memory, of processor time and ofother resources for various tasks

Accessing data from secondary storage

Writing data to secondary storage

Booting a computer loading the OS from disk intomemory

Computer Software

Application Software

Application software used for a specific task

such as word processing, accounting, or

database management.

i.e

Microsoft Word

Microsoft Excel

Microsoft Access

Web browser, Opera, Mozilla etc.

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Computer Software

Computer Languages

Three (3) types of computer languagesMachine language

Binary number codes (0 and 1) understood by a specific CPU

Assembly language

Mnemonic codes that correspond to machine languageinstructions

High-level language

Machine-independent programming language that combinesalgebraic expressions and English symbols

Compiler is used to translate a high-level

language program into machine language

Computer Software

Machine Language vs. Assembly

LanguageMemory Addresses Machine LanguageInstructions

Assembly LanguageInstructions

00000000 00000000 CLA

00000001 00010101 ADD A

00000010 00010110 ADD B

00000011 00110101 STA A

00000100 01110111 HLT

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Computer Software

High-Level LanguagesLanguage Application Area

FORTRAN Scientific Programming

COBOL Business Data Processing

LISP Artificial Intelligence

C Systems programming

Prolog Artificial Intelligence

Ada Real-time distributed systems

Smalltalk Graphical user interface; Object oriented(OO) programming

C++ Supports OO programming

Java OO & Support web programming

Writing programs

Programmers - write programs to instruct the

computer what to do

Various languages C++, Visual Basic, Java, C#,

Phyton, PHP, HTML, Pascal

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Writing programs

What happens when you write a program?

Entering, Translating and Running a

High-Level Programming Language

Documents

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