Introduction to computers

                            COMPUTER SYSTEMS ―A Computer is an electronic device that stores, manipulates and retrieves the data.‖ We can also refer computer computes the information supplied to it and generates data. A System is a group of several objects with a process. For Example: Educational System involves teacher, students (objects). Teacher teaches subject to students i.e., teaching (process). Similarly a computer system can have objects and process.

The following are the objects of computer System

a) User ( A person who uses the computer)

b) Hardware

 c) Software

 Hardware: Hardware of a computer system can be referred as anything which we can touch and 

feel. 

Example : Keyboard and Mouse.

 The hardware of a computer system can be classified as 

👉Input Devices(I/P) 

👉Processing Devices (CPU)

 👉Output Devices(O/P)

ALU: It performs the Arithmetic and Logical Operations such as

      +,-,*,/ (Arithmetic Operators)   

 &&, || ( Logical Operators)

CU: Every Operation such as storing , computing and retrieving the data should be governed by the control unit

MU: The Memory unit is used for storing the data.

 The Memory unit is classified into two types.

 They are

1) Primary Memory

 2) Secondary Memory 

                 Primary memory:

ROM: It represents Read Only Memory that stores data and instructions even when the computer is turned off. The Contents in the ROM can‘t be modified once if they are written . It is used to store the BIOS information.

RAM: It represents Random Access Memory that stores data and instructions when the computer is turned on. The contents in the RAM can be modified any no. of times by instructions. It is used to store the programs under execution.

Cache memory: It is used to store the data and instructions referred by processor.

Secondary Memory: The following are the different kinds of memories Magnetic Storage: The Magnetic Storage devices store information that can be read, erased and rewritten a number of times.

 Example: Floppy Disks, Hard Disks, Magnetic Tapes

Optical Storage: The optical storage devices that use laser beams to read and write stored data. Example: CD(Compact Disk),DVD(Digital Versatile Disk)

COMPUTER LANGUAGES

 To write a program (tells what to do) for a computer, we must use a computer language. Over the years computer languages have evolved from machine languages to natural languages. The following is the summary of computer languages 

👉1940‘s -- Machine Languages

👉1950‘s -- Symbolic Languages 

👉1960‘s -- High Level Languages

 Machine Language

In the earliest days of computers, the only programming languages available were machine languages. Each computer has its own machine language which is made of streams of 0‘s and 1‘s. The instructions in machine language must be in streams of 0‘s and 1‘s. This is also referred as binary digits. These are so named as the machine can directly understood the programs

Advantages:

 1) High speed execution 

2) The computer can understood instructions immediately

3) No translation is needed.

 Disadvantages:

1) Machine dependent

2) Programming is very difficult 

3) Difficult to understand 

4) Difficult to write bug

Example   Additon of two numbers

                                 2           0 0 1 0                         

                         +      3           0 0 1 1   

                                 ---  ---------------  

                                 5            0 1 0 1

                                 ---  --------------- 

                            Symbolic Languages (or) Assembly Language  

In the early 1950‘s Admiral Grace Hopper, a mathematician and naval officer, developed the concept of a special computer program that would convert programs into machine language.  These early programming languages simply mirrored the machine languages using symbols or mnemonics to represent the various language instructions.  These languages were known as symbolic languages.  Because a computer does not understand symbolic language it must be translated into the machine language.  A special program called an Assembler translates symbolic code into the machine language.  Hence they are called  as Assembly language.

Advantages: 

 1) Easy to understand and use 

 2) Easy to modify and isolate error

 3) High efficiency

 4) More control on hardware

Disadvantages: 

 1) Machine Dependent Language

 2) Requires translator

 3) Difficult to learn and write programs 

 4) Slow development time

 5) Less efficient Example