Computer System and I/O Devices

  1.2.1. Concept of computer architecture

The theoretical concept behind the design of computer is called computer architecture.

·         Concept of computer organization

The subject which deals with about the work, which can be performed by computer system, is called computer organization.

·         Components of computer system

  Definition of Computer System:

The integration of different computer parts such as keyboard, mouse, monitor, CPU etc to form an entire system to work effectively and efficiency is called Computer System.

 

   

v Block diagram of computer system

 

 

Input Devices	CPU	Output Devices
	Memory

 

 

1.2.2 Component of Computer System

a)    Input device

An electromechanical device that allows the user to feed data and instruction into the computer for analysis, storage, and to give commands to the computer is called input device.

 

An input device performs the following functions.

i)   It accepts or reads the data and instructions from the user.

ii)   It converts these inputs in the computer acceptable form i.e. binary code.

iii)       It supplies the converted inputs to the computer system for further processing which are stored temporarily in RAM.

 

The keyboard is the most commonly used input devices. Various input devices which do not require typing of information have also been developed i.e. mouse, joystick, touch pad etc. which are called pointing device.

Examples of input devices are keyboard, mouse, joystick, Trackball, Touch screen, Light pen, Touch pad etc.

 

b)    CPU (central processing unit)

CPU is the main part of computer that controls the overall operations of a computer and interprets program and activates necessary components of ALU for execution of a program. The CPU executes programs (instructions) stored in main memory. It takes input from the input device or memory and sends output to the output device or stores to the memory. CPU contains of ALU, CU, and Registers.

i)    Arithmetic logic unit (ALU)

It is responsible for doing all types of arithmetic operations like addition, subtraction, multiplication and division on integer and real operands. It also can be perform logical operation or comparison like equal to, greater than, less than etc. between two operands. It receives its operands from the register section of the CPU and stores its results back in the register section.

ii)    Control unit (CU)

The control unit of the microprocessor co-ordinates and controls the various operations and indicates the appropriate sequence of micro-operation for each task. It controls and guides the interpretation, flow and manipulation of all data.

 

It is responsible for executing the instruction of the program and fetching the data required for the next instruction from memory. It also controls and coordinates the functions of all other units of the computer and ensures smooth operation.

It is mainly responsible for the following:

·      Data exchange of CPU with the memory or input/output components.

·      Internal operations in the CPU such as moving data between registers.

·      Making ALU perform a particular operation on the given data.

·      Regulating other internal operations.

·      Generate control mechanism to hardware and software.

 

iii)     Register

Electronic memory chips made from transistors and flip-flop which serve as temporary storage location in the CPU are called registers.

·      A semiconductor device used to amplify and switch electronic signals and electrical power is called transistor.

·      The memory element most frequency used in sequential circuit is called

Flip-Flop.

The instructions execution is performed in the CPU by taking data from registers. Registers quickly accept, hold and transfer the data and instruction which are being executed currently. The size and number of these registers determine the overall speed of the computer.

The length of a register equals the number of bits it can store. Hence a register that can store 8 bit is called an 8-bit register. Most CPUs sold today have 32-bit or 64-bit registers the length of the register of a computer is sometimes called its word size. The bigger the word size, the faster a computer can process a set of data with all other parameters being same, a CPU with 32-bit registers can process data twice as large as one with 16-bit registers.

 

Registers in CPU are of two types:

1.      Specific Purpose Register (SPR)

2.      General Purpose Register (GPR)

 

Some examples of CPU specific purpose registers are:

·         Memory Buffer Register (MBR) to hold data.

·         Memory address Register (MAR) to hold address.

·         Program Counter Register (PCR) to hold next instruction to be fetched and executed.

·         Stack pointer Register (SPR) to hold address of top of stack memory. Stack is temporary storage area where data is stored temporarily during execution in Last In First Out (LIFO) order.

Other general purpose registers are:

·      Accumulator (Acc) to be used in arithmetic calculation.

·      Counter Register (CX) to count number of repetition of execution.

·      Base Register (BX) to store base address of data.

·      Scratch pad registers to hold operands and result.

The functions of the CPU (Processor) are:

·         To carry out processing.

·         To give commands to all parts of the computer system.

·         To control the sequence of operation.

·         To control the storage of data or instructions.

·         To perform arithmetic calculations such as addition, subtraction etc as well as logical operations such as AND, OR, NOT operation.

 

c)    Memory / Storage

The memory is the computers storing area. This is the place where our data and programs get stored before processing and the result also stored before to its output. Data and instructions are stored in memory in the binary form. Bit is the smallest unit of computer data. The combination of 8 such bits is called a byte. Each byte is also referred to as a single character.

The memory which can retain its memory contents only while the computer is running is called volatile memory. The volatile memory loss its contents after the computer are shut down. It serves for temporary purpose. RAM and cache memory are the examples of volatile memory devices in computer system.

 

The memory which can retain its memory contents even after the computer is shut down is called Non-Volatile memory. The non-volatile memory does not lose its contents after the computer is shut down. It serves for permanent purpose. ROM, Hard disk, CD, DVD etc are the example of non-volatile storage devices of computer.

Only the data and instruction which are being processed and the currently running program are stored in RAM which is also called the memory or main

memory of computer system. The main memory in computer is always limited very fast and very expensive in comparison to secondary storage.

Since RAM is volatile, computer system has a separate memory place to permanently save the data, information, programs etc for future use and it is called secondary storage. The examples of secondary storage are Hard disk, Floppy disk, CD, DVD etc.

d)    Output Device

The device which shows the results of processing and other information from the computer to the human understandable language form is called output device.

The functions of output device are as follows:-

1)     It accepts the result produced by the computer which is in binary form.

2)     It converts binary form of results to human understandable form.

3)     It shows the converted results to the user. Computer output can be classified into two forms:-

 

Soft Copy Output		Hard Copy Output
1.	An output which is in unprinted	1.	An output which is in printed form
digital document file is called soft		is called hard copy output.
copy output.
2.	It is a temporary form.	2.	It is a permanent form.
3.	It can be viewed through an	3.	It cannot be viewed through any
appropriate editing program such as		program.
Microsoft Word, PowerPoint etc.
4.	It can be edited.	4.	It cannot be edited.
5.	It can be transported from one	5.	It cannot be transported from one
computer to another through email or		computer to another very easily.
through USB drives and other disk
drive.
6.	Example:-Any file is saves in	6.Examples:- Computer file printouts,
computer.		fax pages, photo prints etc.