Lesson 1b: Computer Systems and Program Development

CPS118

Objectives

What Is a Computer?

What is an algorithm?

Computer Components

Binary number system

Software Development Method problem solving

Computer Systems Computers are electronic systems that can

transmit, store and manipulate information (data).

Data can be numeric, character, graphic and sound.

For beginner programmers, the two most important are character and numeric.

To manipulate data, a computer needs a set of instructions called a program.

To write such programs is the object of this course.

Computer

An electronic machine that can receive, store, transform, and output data of all kinds numbers, text, images, graphics, and sound, to name a few.

Algorithms An algorithm is a series of instructions on how to

solve the problem.

An algorithm is a finite set of instructions which, if followed, accomplish a particular task.

Computing definition: A computable set of steps to achieve a desired result.

Characteristics of algorithms

Algorithms have the following characteristics: Precision

Uniqueness

Finiteness

Input

Output

Generality

Criteria of algorithm

must satisfy the following: input:

there are 0 or more quantities which are externally supplied;

output: at least one quantity is produced;

definiteness: each instruction must be clear and unambiguous;

finiteness: for all cases the algorithm will terminate after a finite

number of steps; effectiveness:

every instruction must be sufficiently basic it can in principle be carried out by a person using only pencil

and paper.

A friend come to visit you:

The taxi algorithm: Go to the taxi stand. Get in a taxi. Give the driver my address.

The call-me algorithm: When your plane arrives, call my cell phone. Meet me outside baggage claim.

The rent-a-car algorithm: Take the shuttle to the rental car place. Rent a car. Follow the directions to get to my house.

The bus algorithm: Outside baggage claim, catch bus number 70. Transfer to bus 14 on Main Street. Get off on Elm street. Walk two blocks north to my house.

Algorithm Example

Input (what is needed by the program): n Output (the value computed by the

program): 1/1+1/2+...+1/n

1. answer=0 (initialize the answer at 0) 2. d=1 (start the denominator at 1) 3. answer=answer+1/d (adding 1/d to the

previous answer) 4. d=d+1 (adding 1 to the denominator) 5. repeat lines 3 and 4 until d is equal to n

Computer Systems

3 types of computer systems:

Mainframes and minicomputers

Workstations

Personal computers PCs

Laptops

Components of a Computer

Computer Components

Central Processing Unit

Main Memory

ALU CU

CD

zipdisk

floppydisk

SecondaryStorage:

mouse

monitor

keyboardharddisk

printer

scanner

Input & Output Devices

Computer System

CPU + Main Memory ~ “core” Secondary Storage + I/O Devices ~ “peripherals” Bus ~ communication between components

CPU

Sec. Storage

I/O 1

I/O 2

I/O n

Memory

Bus

Storage Types

CPU Registers: Only a few cells on CPU

Main memory (RAM): Millions of cells on circuits separate from CPU.

Secondary storage: Billions of cells on disks or tapes.

Secondary storage is not volatile.

Internal representationsBit: Binary digit (0 or 1).

Byte: A group of 8 bits. One character.

Word: The width of a memory cell.

Each byte of main memory has an address.

All numbers are represented in binary.

Integer numbers NOTE: The following number representations are simplified. They do not

represent the actual pattern inside most computers.

All numbers are converted in binary:

ex: 9 = 1001

In a computer system, the leftmost bit is the sign bit (0 is positive, 1 is negative).

So 9 in a 32 bit system would be:00000000000000000000000000001001

Real numbersReal numbers in binary are expressed with a

mantissa, a base and an exponent.For a real number , the mantissa is defined as the positive fractional part

Suppose 9.0 in binary:In 32 bits a simple view isbit sign=0base and exponent=16 (base=2, exponent=4).mantissa=9/16=0.5625for 32 bit float number (8: exp, 23 mantissa):0 00000100 10010000000000000000000

32 bit real number

1: 0 00000001 10000000000000000000000 2: 0 00000010 10000000000000000000000 3: 0 00000010 11000000000000000000000 4: 0 00000011 10000000000000000000000 5: 0 00000011 10100000000000000000000 6: 0 00000011 11000000000000000000000 7: 0 00000011 11100000000000000000000 8: 0 00000100 10000000000000000000000 9: 0 00000100 10010000000000000000000

32 bit real number cont’d

10:000000100 10100000000000000000000 11:0 0000010010110000000000000000000 12:0 0000010011000000000000000000000 13:0 0000010011010000000000000000000 14:0 0000010011100000000000000000000 15:0 0000010011110000000000000000000

16:0 000010001000000000000000000000

Real numbersA double number is expressed in 64 bits:52 bits for the mantissa, 11 bits for the

exponent and 1 sign bit.

Exponent: right to left, like an integer.Mantissa: left to right, 0.5, 0.25, 0.125,

0.0625,... and so on. 1 if needed, 0 if not.

So 9.0 is: 0000000001001001000000000000000000000000000000

000000000000000000

CharactersCharacters are expressed using the ASCII

code:A = 65 = 01000001g = 103 = 01100111$ = 36 = 00100100+ = 43= 00101011

See code here:http://www.asciitable.com/

Programming LanguagesGeneration 1: Machine languages (pure

binary)101011101010101010111010101011

Generation 2: Assembly languages (mnemonic codes)

MV R1,R3

Generation 3: High-Level Languages (C, Fortran, Java)

Solving Problems1. Define the problem

2. Analyse the problem.

3. Design a solution.

4. Implement the solution.

5. Test the program.

6. Update and maintain the program.

ImplementationHere is a detail of step #4, implementation

(actual programming):

4.1 Write the program source.

4.2 Compile the source code and check for errors.

4.3 Link the code with libraries and build the program.

4.4 Run the program.

Why C?1. It is portable.

2. It is efficient.

3. It is easy to learn.

4. It is modular.

5. It is widespread.

Summary

Computer

algorithm

Computer Components

Binary number system

Software Development Method problem solving

End of lesson