COMPUTER SYSTEM

COMPUTER SYSTEM

Block Diagram of Computer Architecture

Hardware

The physical equipments and components of a computer that can be seen, touched and felt are collectively called hardware. Hardware components are important aspects of a computer system that performs the tasks of entering data and instructions, executing instructions, processing data, storing data and giving output in displayed or printed form.
There are four types of hardware. They are:

• Input unit
• Processing Unit
• Output Unit and
• The Storage Unit.

Input Unit:

•  Input refers to any means that moves data (information) from the outside world into the processor.
• Before computer processes, data must be entered into the computer by an input device so that they can be translated into a machine-readable form.
• Input unit involves the devices through which data or instructions are entered into the computer for further computation.
• Input devices are the means through which the users communicate with the computer.
• Example: keyboard, mouse, joysticks, scanner, etc.

Processing Unit or Central Processing Unit (CPU)

 A microprocessor is an integrated circuit that contains a complete CPU on a single chip. The CPU is the brain of the computer, the place where data is manipulated. The CPU is the component of a computer system with the circuitry to control the interpretation and execution of instructions. It performs the process part of INPUT-PROCESS-OUTPUT cycle. It temporarily stores current data and instructions, performs computation executing the instructions and controls the activities of the entire parts of a computer system by transferring information between its entire parts. It is called electronic brain of computer since its different sections perform tasks of memorizing data and instruction, making calculations, making logical decisions and controlling activities of entire parts of a computer system electronically as different parts of human brain do biologically.
CPU has at least two basic parts:

Control Unit

•  The Control Unit interprets any instruction it receives from memory and directs the sequences of events necessary to execute the instruction.
• It provides status, control and living signals necessary for other parts of the CPU, memory and input/output devices
• Control unit uses a system clock which synchronizes all tasks by sending out electrical pulses. Each instruction takes a specific number of system clock cycles to complete. The same instruction may take ten clock cycles to complete on one processor but only five clock cycles on another.

Arithmetic and Logic Unit (ALU)

• ALU is that part of CPU where actual data processing occurs. All mathematical calculations and all comparisons (logic function) take place in this unit.
• Every arithmetic step requires at least two numbers and then it produces a result.
• In addition to arithmetic functions, ALU also performs logic functions. A logic function is one where numbers or conditions are compared to each other.
• When control unit encounters an instruction that involves arithmetic or logic, however, it passes that instruction to the ALU unit.
• The ALU includes a group of registers, high speed memory locations built directly into the CPU that are used to hold the data currently being processed.

Output Unit / Output Devices

•  Output unit involves the devices through which information resulted by the processing is given to the users.

• The output devices receive the information from the CPU in binary form and then convert and give it in users' understandable form.
• An output device allows a computer to communicate information to the user or another machine by accepting data from the computer and transforming them into a usable form.
• Output is divided into two general categories:
  • Output that can be readily understood and used by users.
  • Output to secondary storage devices that hold the data to be used as input for further processing by computer.
• Output that can be understood by users can be in the form of soft copy and hard copy.

Soft copy output devices:

• Softcopy output devices are such output devices which give temporary output in the displayed form.
•  An output on soft copy devices enables viewing of the work which allows corrections or rearrangement of material to suit specific needs.
• The most commonly used soft copy device is a monitor.
• Some others are Visual Display Unit (VDU), Liquid Crystal Display (LCD), Light Emitting Diode (LED), etc.

Hard copy Output devices:

• Hard Copy output is output on paper and can be read immediately or stored and read later.
• This is a relatively stable and permanent form of output.
• Hard-copy output devices are those devices which give the permanent output in the printed or recorded form. Some of the examples include printers, plotters etc.

Storage Unit and Storage Device

• A Storage Device is that which contains data either temporarily or permanently.
• There are two types of Storage devices, namely - Temporary Storage Device or Primary Storage Unit and Permanent Storage Device or Secondary Storage Unit.
• Examples: Hard Disk, Floppy Disk, CD, DVD, Flash Drive, etc.

Primary Storage or Main Memory:

• Main memory is the principle internal memory system of the computer.
• It is a temporary storage area where the program and data being operated on by processor must reside.
• Main memory is considered temporary because that data program will remain there only as long as the computer has electrical power or is not reset.
• Example: RAM and ROM.

Posted By:	Mr. Lohala		Submitted on:	Tuesday, 14 December 2010