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, 17 th century

Leibnitz’s Wheel, 17 th century

Jacquard Loom, 19 th century

Difference Engine, 1823

Herman Hollerith, 1890

ABC, 1939

ENIAC, 1946