Chapter I: Introduction to Computer Science

Computer: is a machine that accepts input data, processes the data and creates output data.

This is a specific-purpose concept of computer

What is computer?

• Today’s computer is general purpose machine “Programmable computer”

• A program is a set of instructions that tells the computer what to do with data.

• Early days, computer program used to be implemented by changing the wiring or turning a set of switches on and off. Today, a program written in computer language

• In programmable computers, the output data depend on:

1. The Input data

2. The program

Von Neumann Model• Named after John von Neumann• Von Neumann Model consists of:1. Memory: storage area, where programs are

stored during processing.2. Arithmetic Logic Unit (ALU): where calculations

and logic operations take place.3. Control Unit: Controls the operation of memory,

ALU and input/output subsystems.4. Input/Output: Input units accept input data(e.g.

keyboard….). While output units demonstrate output data ( monitor….)

Von Neumann Model

Von Neumann, EDVAC, 1950

Stored Program Concept• Von Neumann model states that program

must be stored in memory unlike early computer where only data are stored.

Sequential Execution of Instructions• Control Unit executes the set of a program’s

instructions one after another (sequentially)

Computer Hardware• Computer Hardware Must include all four

parts of von Neumann Model

Data Storage and Organization• Data storage:– Data stored as electrical signal.– Computer stores data in Binary form (0,1).– All sort of input data must be transferred into binary

data.

• Organizing Data:– Data are organized into small units, small units are

organized in larger units.

Computer software

According to Von Neumann Model: • Program must be stored in the memory.• Program must be a sequence of instructions• Program is made of instructions• Instructional format of programming support

“reusability” of programming in different platforms.

Algorithms• In order to structure a program to solve a specific

problem, computer programmer must break down the program into steps, each step is an instruction, those step-by-step solution is called algorithms

Language• Computer language is (in concept) similar to

human language, though very limited.• Computer language is made of set of symbols

each symbol represents an instruction.

Software Engineering• Is the design of structured programs following

strict principles and rules of programming languages.

Operating Systems• Works as an interface between computer

program and computer componants.

Pascaline, 17th century

Leibnitz’s Wheel, 17th century

Jacquard Loom, 19th century

Difference Engine, 1823

Herman Hollerith, 1890

ABC, 1939

ENIAC, 1946