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# What is a computer by bigbro22

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```									Lecture 1
Introduction

Input             Computer               output

What is a computer?
A computer accepts external input , processes the
data, and produces certain output .
An algorithm is a \recipe" for processing information
| a series of steps that transform input to output.

1
LECTURE 1.   INTRODUCTION                         2

1.1 Basic Computer Architecture

Control   Arithmetic   I/O
Unit        Unit      Unit

Input                                         output

Memory

Secondary
Storage
LECTURE 1.   INTRODUCTION                                     3

Key Elements in a Computer
Input Unit:
{ Obtains information (data and programs) from
various input devices, such as keyboard and disk
drive.
Output Unit:
{ Places processed information onto various output
devices, such as screen or printer.
Memory Unit:
{ Retains information entered from the input unit.
{ Stores programs.
{ Stores intermediate results during processing.
Arithmetic and Logic Unit (ALU):
{ Performs actual calculations and comparisons.
Control Unit:
{ Supervises and coordinates the entire operations
of a computer.
Secondary Storage:
{ A device, such as tapes or disks, for storing pro-
grams or data that are not actively being used by
other units.
LECTURE 1.     INTRODUCTION                                                        4

0 1 0 0 0 0 0 1                (represents character ‘A’)

bit
0000           0001     0002            0003
byte
0004

......
Memory
......

Memory Organization | Bits & Bytes
In the lowest level, computers understand only 0's and
1's.
Computer memory stores a sequence of 0's and 1's.
Each such storage unit is called a bit .
Eight bits are grouped together to form a larger stor-
age unit called a byte .
Each byte has a unique address for identi cation.
Computer memory can thus be viewed as a series of
bytes.
LECTURE 1.        INTRODUCTION                                         5

1.2 Computer Programming

Computer Programming
The job of a programmer is to design a complete and
precise set of instructions for a computer to carry out
A programming language is a medium for program-
mers to express instructions to the computer.
Do we need to write our programs in 0's and 1's?!

Compiler                   Computer
Language

Input

High Level Programming Languages
Fortran, Cobol, Pascal, Modula-2, Ada, C, Smalltalk,
C++, Prolog, Lisp, Perl, Java, Visual Basic, ...
Compilation: High level languages require the use of a
compiler to translate into machine executable codes.

2 End.

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