Components of a computer system

ITEC 1000 Introduction to Information Technologies 1

Components of a computer system• Data = information

– stored - where ? (hardware)– manipulated - by whom (software)– examples (resume, list of contacts, employees,

documents, graphics, sound, …)• Hardware• Software• Communication component

Sunday, September 27, 2009

http://www.yorku.ca/yorkweb/index.htm



Hardware types

• I/O devices: – Monitor, keyboard, mouse, speakers– Storage: floppy disks, zip drives, hard disks, CDs

• The box– CPU (one or more); CPU =

• Arithmetic and Logic Unit• Control Unit• Interfaces

– Memory (RAM)– I/O interfaces– buses





Schematic representation





Another view





Memory• Memory = storage cells • Each cell can store a character• 1 cell = 8 bits = 1 byte• 1 Kilo Byte = 1024 bytes• 1 Mega Byte = 1024 KB• 1 Giga Byte = 1024 MB





• Similar cells in the hard drives, memory sticks, ZIPs• Can store data and or program instructions

– Instruction = the most basic operation – 1 instruction is stored on 1, 2 or 3 bytes





Software

• Software = computer programs• Program = set of instructions defining

– Data to be manipulated– Logic for manipulating it

• Types– System software– Application software





Operating systems • Examples: Unix, Linux, Windows, Mac OS X• Executive functions - tells various parts what to

do• Becomes activated as soon as the computer starts

(booting time)• Main functions:

– manage computer data flow– manage user-computer interaction– manage other programs– manage files

• Has many components, solves general tasks





Programming Languages

A programming language is an artificial language used forexpressing operations that a particular machine can execute

The operations may include:• mathematical computations, • logical operations that compare sets of data, • operations that allow the machine to communicate with the worldThe machine need not be a “computer” e.g.: • milling machine• player piano• automated manufacturing





Computer Programming Language

A language for expressing operations that can be used to solve problems that use resources of a computer

A computer language is able to translate expressed operations into the 1’s and 0’s that make up the machine version of the expressed operations.

Examples: • C • fortran, • java





Application software

• Software (programs) which are run by the operating system (OS)

• Usually is not as evolved as the OS• Solves specific user tasks• Ex: Word, Netscape, IE, graphics viewers, music

players, chatting programs• Can range from very easy to very complex• Can be developed using different computer

languages





OS components

• API (Application Programming Interface) – set of software components, used by application programs to access OS functionality

• Kernel: system management• Services: specific major OS functions• File management

– All data is stored in files or databases– Manages files

OS components stored in ROM - started at boot time





Communication• Computer communicate with each other• Networks• Required components:

– Hardware– Software

• Computers can communicate with each other, independently of their size

• The field where most of the future action will take place





Inside “The Box”





Motherboard





CPU(Central Processing Unit)





SIMM(Single Inline Memory Module)





HDD(Hard Disk Drive)





Power Supply





Schematic Diagram of a Personal Computer





Ports

CPU

RAM

Diskcontroller

Graphicscard

Soundcard

Networkcard

Printer

Mouse

Keyboard

ModemMonitor

Speakers

bus

Computer





DATA FORMATS AND INPUT





Figure 3.1 Data conversion and representation

Data input





Examples

Real World

Data

Computer

DataInput device





Examples

Real World

Data

Computer

DataInput device

Dear Mom: Keyboard 10110010…





Examples

Real World

Data

Computer

DataInput device

Dear Mom: Keyboard 10110010…

Digitalcamera

10110010…





Rules/Conventions

• Proprietary formats– Unique to a product or company– E.g., Microsoft Word, Corel Word Perfect, IBM Lotus

Notes• Standards

– Evolve two ways:• Proprietary formats become de facto standards (e.g., Adobe

PostScript, Apple Quick Time)• Committee is struck to solve a problem (Motion Pictures Experts

Group, MPEG)





Standards Organizations

• ISO – International Standards Organization• CSA – Canadian Standards Association• ANSI – American National Standards Institute

• IEEE – Institute for Electrical and Electronics Engineers




http://en.wikipedia.org/wiki/International_Organization_for_Standardization

http://en.wikipedia.org/wiki/International_Organization_for_Standardization

http://www.csa.ca/Default.asp?language=english

http://www.csa.ca/Default.asp?language=english

http://en.wikipedia.org/wiki/American_National_Standards_Institute

http://en.wikipedia.org/wiki/American_National_Standards_Institute

http://en.wikipedia.org/wiki/Institution_of_Engineering_and_Technology

http://en.wikipedia.org/wiki/Institution_of_Engineering_and_Technology


Examples of Standards

Type of Data Standards Alphanumeric ASCII, EBCDIC, Unicode

Image JPEG, GIF, PCX, TIFF, PNG

Motion picture MPEG-4, Quick Time

Sound WAV, AU, AIF, MIDI, MP3 Outline graphics/fonts

PostScript & PDF





Why Standards?• Standards are “arbitrary”• They exist because they are:

ConvenientEfficientFlexibleAppropriate

Plus, they provide some consistency andpredictability for applications.





Alphanumeric Data

• Problem: Distinguishing between the number 123 (one hundred twenty-three) and the characters “123” (one, two, three)

• In software: data is given a type• Three standards for representing letters (alpha) and

numbers– ASCII – American standard code for information interchange– EBCDIC – Extended binary-coded decimal interchange code– Unicode



The Problem

• Representing text strings, such as “Hello, world”, in a computer

After all, computers store binary digits, not letters!





ASCII codes and characters

• Each character is coded as a byte• Most common coding system is ASCII (Pronounced

ass-key)• ASCII = American National Standard Code for

Information Interchange• Defined in ANSI document X3.4-1977





ASCII originsASCII codes developed to represent numbers, letters, and control codes.

Originated from prior codes for telegraph transmission known as Morse Code - which similarly had to represent data with strings of short and long electrical pulses

Morse Code the invented 1840’s and was basis of all telegraph transmission through first half of 20th century

More Morse Code




http://en.wikipedia.org/wiki/Morse_code

http://en.wikipedia.org/wiki/Morse_code


Lengths of the pulses depended on the operator and could lead to errors in interpretation.

Automatic uniform method achieved with modification of the Baudot code - eventually using a keyboard method Adopted by Western Union - prevalent thru 1950’s.

Baudot code equivalent to 5 bit code of 0’s and 1’s - where a short pulse interpreted as 0 and a long pulse as 1.




http://en.wikipedia.org/wiki/Baudot_code

http://en.wikipedia.org/wiki/Baudot_code


• ASCII code developed from Baudot code - as 7 bit sequences of 0’s and 1’s . Promoted by Bell data services as codes for a teleprinter.

• 7 bits gives 27 = 128 possible codes 95 for characters that appear on screen or are printable 33 that are control characters - some obsolete telegraph codes

• An 8th bit used later for various extended character sets





ASCII chart0 1 2 3 4 5 6 7

0 NULL DLE 0 @ P ` p1 SOH DC1 ! 1 A Q a q2 STX DC2 " 2 B R b r3 ETX DC3 # 3 C S c s4 EDT DC4 $ 4 D T d t5 ENQ NAK % 5 E U e u6 ACK SYN & 6 F V f v7 BEL ETB ' 7 G W g w8 BS CAN ( 8 H X h x9 HT EM ) 9 I Y i yA LF SUB * : J Z j zB VT ESC + ; K [ k {C FF FS , < L \ l |D CR GS - = M ] m }E SO RS . > N ^ n ~F SI US / ? O _ o DEL

This is a hexadecimal table - with high digit (leftmost) indicated by column and the low digit (right most) by the row. The letter “a” in hex is then 61, or in binary 110 0001





Code types: 95 graphic codes0 1 2 3 4 5 6 7


See Wikipedia article history of ASCII




http://en.wikipedia.org/wiki/ASCII

http://en.wikipedia.org/wiki/ASCII


Code types: 33 control codes0 1 2 3 4 5 6 7






“Hello, world” Example

============

Hexadecimal48656C6C6F2C207767726C64

Decimal721011081081114432119103114108100

Hello,

world

============





Common Control Codes in hex

• CR 0D carriage return

• LF 0A line feed

• HT 09 horizontal tab

• DEL 7F delete

• NULL 00 null





Common control codes in table0 1 2 3 4 5 6 7


Description of all control sequences




http://www.cs.tut.fi/~jkorpela/chars/c0.html

http://www.cs.tut.fi/~jkorpela/chars/c0.html


Escape and control sequences

• Extend the capability of the ASCII code set• For controlling peripheral devices and formatting output• Defined by ANSI in documents X3.41-1974 and X3.64-1977

An escape sequence consists of 3 parts

• escape sequence introducer = ESC = 1B hex • intermediate characters (1 or more) in 2nd column of hex table

• final character - from columns 3-7 of hex table





A control sequence consists of 4 parts

• control sequence introducer - 2 hex characters ESC = 1B and [ = 5B

• parameter characters - ( 0 or more) from column 3• intermediate characters - (0 or more) from column 2• final character from columns 4 thru 7

ESC [ 3 g = clear tabs

ESC [ ? 4 h = set smooth scroll mode

ESC [ 2 , 1 y = invoke self-test

Examples

ESC [ 2 J = erase displayESC [ K = erase line





EBCDIC

• Devised in 1963 and 1964 by IBM for the IBM System/360 line of mainframe computers.

• Most IBM mainframe peripherals and operating systems use EBCDIC

• Created to extend the Binary Encoded Decimal system for encoding numbers (to be covered later)

• 8-bit character encoding, with 28 = 256 possible encoded characters

• Different from 7 bit ASCII encoding




http://en.wikipedia.org/wiki/System/360

http://en.wikipedia.org/wiki/System/360


• Punch cards now obsolete and EBCDIC now used for backward compatibility

• settled on EBCDIC as solution

• IBM had been a chief proponent of the ASCII standardization

• IBM did not have time to prepare ASCII peripherals (such as card punch machines) to ship with System/360 computers

• entering data with punch cards easy with EBCDIC

More EBCDIC




http://en.wikipedia.org/wiki/Punched_cards

http://en.wikipedia.org/wiki/Punched_cards

http://en.wikipedia.org/wiki/EBCDIC

http://en.wikipedia.org/wiki/EBCDIC


Unicode

An evolving 16 bit standard - most recent update only months ago - possibility of 216 = 65,536 different codes at one time

Unifies 100’s of different and conflicting encoding systems

Characters cover the principal written languages of the Americas, Europe, the Middle East, Africa, India, Asia, and Pacifica.





Joe Becker from Xerox ,Lee Collins and Mark Davis from Apple investigated idea of a universal character set.

Origins of Unicode - 1987

Unicode is intended to address the need for a workable, reliable world text encoding. Unicode could be roughly described as "wide-body ASCII" that has been stretched to 16 bits to encompass the characters of all the world's living languages. In a properly engineered design, 16 bits per character are more than sufficient for this purpose.

Most work completed by 1990

Becker in draft proposal writes




http://en.wikipedia.org/wiki/Joe_Becker_(Unicode)

http://en.wikipedia.org/wiki/Joe_Becker_(Unicode)

http://en.wikipedia.org/wiki/Xerox

http://en.wikipedia.org/wiki/Xerox

http://en.wikipedia.org/wiki/Mark_Davis_(Unicode)

http://en.wikipedia.org/wiki/Mark_Davis_(Unicode)

http://en.wikipedia.org/wiki/Apple_Inc.

http://en.wikipedia.org/wiki/Apple_Inc.


Initial focus on existing languages

Unicode gives higher priority to ensuring utility for the future than to preserving past antiquities. Unicode aims in the first instance at the characters published in modern text (e.g. in the union of all newspapers and magazines printed in the world in 1988), whose number is undoubtedly far below 214 = 16,384. Beyond those modern-use characters, all others may be defined to be obsolete or rare; these are better candidates for private-use registration than for congesting the public list of generally-useful Unicodes.

Not the case:• many historic scripts and thousands of rarely-used/obsolete characters now encoded. • work continues to encode even more(e.g. Egyptian Hieroglyphs).




http://en.wikipedia.org/wiki/Egyptian_hieroglyph




Documents

Components of a computer system