Computer Fundamentals Lecture01 Sri Lanka Institute Of Information Technology (sliit)

Computer Fundamentals Lecture 1: Data Types and Data Representation

03/12/09

Sri Lanka Institue of Information Technology

Course Objectives 

After completing this module students will be able to: Explain fundamental concepts related to computer systems  Identify major components of a computer and describe their functionality  Illustrate how each component work and communicate with each other  Distinguish the functional importance of different components And  Assemble a computer for a given task 

03/12/09

Sri Lanka Institue of Information Technology

Lecture Outline

03/12/09

Sri Lanka Institue of Information Technology

Lecture Objectives 

Data and it’s representation inside computers  

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What do they mean by “data”? Why do we need a representation to hold them inside a computer? Data types and their usage

Sri Lanka Institue of Information Technology

Agenda         

A Modern Computer System What is data ? How do we store them inside a computer? Programmers point of view Basic Data Types Number Representation Floating Point Representation Data Representation in Computers Binary Code Transmission

03/12/09

Sri Lanka Institue of Information Technology

A Modern Computer System

Image Credit: Modern Operating System by Andrew S Tanenbaum 03/12/09

Sri Lanka Institue of Information Technology

A Modern Computer System

Image Credit: Operating System Concepts by Silberschatz et. al. 03/12/09

Sri Lanka Institue of Information Technology

What is data ?      

Data is an observation The physical world is observed by sensors These sensors, upon receiving input signals output a signal These input signals are very often analog in nature Analog signals are continuous electrical signals that vary with time Most of the time, the variations follow that of the non-electric (original) signal, therefore the two are analogous

03/12/09

Sri Lanka Institue of Information Technology

How do we store them in a computer? 

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Computer is a digital device which is capable to handle discrete data/information Therefore, we need to convert these analog signals to digital signals after capturing them by the input devices This is done with the converter ADC Digital signals are represented by numbers Once these numbers are captured they need to be stored in the main memory ( this is a requirement by the architecture)

03/12/09

Sri Lanka Institue of Information Technology

How do we store them in a computer? The main memory is a collection of discrete units called BYTES.  In order to store a lengthy number when it exceeds one BYTE we need a specific way  That is what we call the data representation 

03/12/09

Sri Lanka Institue of Information Technology

How do we store them in a computer?   

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The memory is made up of BYTES Each BYTE can be addressed uniquely When the address is expressed in Binary, the number of maximum BITs used to write the address specifies the total number of locations available If n number of BITs are available then the total number of locations available is 2n If we have 32 BITs then we can have 4GB of Memory

03/12/09

Sri Lanka Institue of Information Technology

How do we store them in a computer? 

Our pc’s are having 512MB of main memory (RAM). How many bits are used to address the memory locations of the PC?

03/12/09

Sri Lanka Institue of Information Technology

How do we store them in a computer? The number used to identify a memory location (which is a BYTE) is called the address.  There is no place given in the memory location to have this address 

03/12/09

Sri Lanka Institue of Information Technology

Programmers point of view     

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Programmers need to use data in their programs The architecture says, it is required to store them in the main memory before use Therefore, it is required to find a way to put them in memory He sets his requirement through what we call a DATA TYPE Through a data type, architecture tells the computer that data must be stored in a particular way in the main memory For that, the data must have a representation

03/12/09

Sri Lanka Institue of Information Technology

Basic Data Types: Character Data 

Numeric 

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Alphabetic 

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012…9 Abc……z

Special 

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(#@%$&…

Sri Lanka Institue of Information Technology

Basic Data Types: Numeric data 

Integer  + & - whole numbers  4251

-582

Most significant bit Least significant bit 

Real  All numbers including everything between integers  0.23, 0, 5 ½, -2.3,

03/12/09

Sri Lanka Institue of Information Technology

Number Representation 

Fixed Point Representation 

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12.548

Floating Point Representation 

Scientific Notation 

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Computer Notation 

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12.054 -> 1.2054 * 101 12.65 -> .1265*102

Sri Lanka Institue of Information Technology

Floating Point Representation Mantissa/argument 15.23 * 10

4

Exponent Radix /base

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Sri Lanka Institue of Information Technology

Data Representation in Computers  

How do computers represent data? Most computers are digital  Recognize only two discrete states: on or off  Computers are electronic devices powered by electricity, which has only two states, on or off

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Sri Lanka Institue of Information Technology

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Data Representation in Computers 

Binary representation  A number system that has just two unique digits, 0 and 1  The two digits represent the two off and on states Binary Digit (bit)

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Electronic Charge

Electronic State

Sri Lanka Institue of Information Technology

Data Representation in Computers 

BCD (Binary Coded Decimal)  4 bit code for numeric values only  9 ->1001

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Sri Lanka Institue of Information Technology

Data Representation in Computers

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ASCII (American Standard Code for Information Interchange)  7 bit code for all 128 characters A=1000001

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EBCDIC (Extended BCD Interchange Code)  8 bit ASCII Sri Lanka Institue of Information Technology

Data Representation in Computers 

ASCII (American Standard Code for Information Interchange)  7 bit code for all 128 characters A=1000001

03/12/09

Sri Lanka Institue of Information Technology

Binary Code Transmission 

Pulse Train

Pulse level High

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Parity bit Parity bit  Even parity Low  Odd parity

ASCII –’ A’ 03/12/09

Sri Lanka Institue of Information Technology

time

Thank You

03/12/09

Sri Lanka Institue of Information Technology