Computer is an electronic machine that is used to solve different kinds of problems according to a set of instructions given to it. Computer consists of different units that perform various functions. All the operations of the computer are controlled by the program instructions. These program instructions are known as software. A system is a group of related components that make up a body to perform a specific function. Therefore computer system is defined as:

The computer along with various units and software that performs different activities in data processing are collectively known a computer system. A computer system is divided into two sub-systems:

1. Computer Software
2. Computer Hardware

Computer Software

A set of instructions given to the computer in machine code that tells the computer what to do and how to perform the given task of the user is known as computer software.

 OR

A set of instructions given to the computer in machine code to solve problems or to control different operations of the computer is known as computer software.

the sofware is developed in computer programming languages. You can not feel, touch or see software inside the computer memory.

Computer Hardware

The physical parts of a computer are known as computer hardware. You can touch, see and feel the hardware. The hardware consists of electronic circuits and mechanical equipment etc. used to perform various functions in the computer. The hardware components are:

1. Input devices
2. Output devices
3. Central Processing Unit (CPU)
4. Memory unit
5. Storage devices

Components of Computer

The internal architechtural design of computers differs from one system model to anohter. However the basic components and their functions are same for all computer systems. The construction of a typical comupter (PC) is very simple. It contains different components. Each components performs a specific function in the computer.

Input Devices

The devices that are used to enter data and instructions into the computer are called input devices or units. In old computers the punched card readers, paper tape readers were used as input devices. Now-a-days the most commonly used input devices are Keyboard and Mouse.

Output Devices

The computer processes the given input data and gives the output. The devices that are used to get output from a computer in readable from are called output devices. A number of output devices are available. Some commonly used output devices are video display units (VDU) and printers.

Central Processing Unit

Central Processing Unit is simply called as CPU. It is the main components of the computer and it is also called the Processor. The processor used in microcomputer is referred to as Microprocessor. CPU is considered the brain of the computer. It performs all operations of data according to program’s instructions. It executes the program instructions and tells other parts of the computer what to do. The CPU fetches instructions of program from main memory and executes them one by one. The CPU also has the ability to decide which instruction will be executed next. The speed of the CPU is measured in Mega Hertz (MHz) or Giga (or more).

The CPU is divided into two main prart of sub-units. These are:

1. Control Unit (CU)
2. Arithmetic Logic Unit (ALU)

1. Control Unit (CU)

The control unit is the most important component of the CPU. It controls and coordinates the activities of all the other units of the computer. The control unit is considered as the logical hub of the computer. It acts as a central nervous system for the other components of the computer.

For example the control unit receives the data and instructions from the input device and stores them in the main memory. It performs all these functions by issuing commands to the relevant unit of the computer.

The control unit also controls the execution of instructions given to the computer. It fetches the instructions and data from the memory unit. It decodes and executes the instructions one by one.

2. Arithmetic Logic Unit (ALU)

Arithmetic Logic Unit or simply ALU is another important component of CPU. It performs the arithmetic and logical operations on the data. When the control unit encounters and instruction related to perform arithmetic or logical operation on data, it passes that instruction to ALU.

• In arithmetic operations ALU performs the addition, subtraction, multiplication and division.
• In logical operations ALU compare the numerical data as well as alphabetic data. For example, it checks whether first number is greater than second, less than second or equal to second etc. It must be noted that some of the logical operations can be done on test data. For example when you want to search a word in a document., the CPU matches each word of the docum ent with the given word. Actually the ALU compares each word of document with the given word through relational equal operator (=).

The ALU consists of a number of registers and adder circuits. A register is a temporary storage device which holds data and instruction as long as it is being interpreted (decoded) and executed. When the data and instructions are fetched from main memory for processing, these have to be stored in one of the registers of the CPU.

RAM stands for Random Access Memory. Actually the main memory or primary storage is referred to as RAM. It consists of memory chips that can be read from and writtern to by the processor. When the computer is powered on, certain operating system files load into RAM from the storage device such as a hard disk. Then operating system remains in RAM as long as the computer has continuous power.

The control unit performs the following functions for main memory.

• Stores the data and instructions (entered from input unit) into the RAM (or main memory).
• Provides the data and instructions from main memory to other parts of the computer.
• Stores the processed results back into the RAM (or main memory).

The RAM plays very important role in data processing. The program and the data must be transferred to RAM before to run the program to process the data. The processor processes the data according to the program instructions by fetching the data and instructions from the RAM. The processor interprets and executes the program instructions while the program is in RAM. During this time the content of RAM may change. RAM can hold multiple programs simultaneously, provided the computer has enough RAM to accommodate all the programs. The program with which you are working usually is displayed on the screen. In Windows environment you can switch from one program to another.

 The storage capcity of RAM or main memory is measured in bytes. A byte is a group of 8-bits. One character takes one byte of memory. The amount of data and program size are also measured in bytes.

The large RAM size increases the accessing speed of the computer. RAM plays an integral part in the internal operation of processor. Microcomputers come with different amounts of RAMs which are from 128MB to 2GB. Advertisements normally list the type of processor, the clock speed of the processor and the amount of RAM in the computer. More RAM means the computer can use powerful program with large size. It also improves the data processing speed of the computer.

Memory Module

RAM chip is smaller in size than the processor chip. A RAM consists of more than one chips. RAM chips usually reside on a memory module which is a small circuit board. Memory slots on the motherboard hold memory modules. There are three types of memory modules. There are:

1. DRAM

DRAM stands for Dynamic Random Access Memory. DRAM is the most common type of RAM used to store data & instructions. In order to maintain data in DRAM chip, the chip is refreshed frequently (hundreds of time a second), otherwise data may be lost. During the refreshing process the CPU has to wait to read & write data in DRAM. It is because DRAM decreases the processing speed of the computer.

Today many DRAM chips exists and most of which are faster than the basic DRAM. The most important are:

SDRAM

SDRAM stands for Synchronous Dynamic RAM. SDRAM are much faster than basic DRAM chips because they are synchronized to the system clock. Often in computer ads, the speed of SDRAM is expressed in megahertz (MHz).

RDRAM

RMRAM stands for Rambus Dynamic RAM. It is faster and more expensive than SDRAM because it uses pipelining technique. It is used in Intel P4. Today most of PCs use SDRAM or RDRAM.

2. SRAM

SRAM stands for Static Random Access Memory. It is faster than DRAM because it does not have to be refreshed frequently and the CPU has not to wait to read & write data. SRAM chips however are more expensive than DRAM chips. Special applications such as cache use SRAM chips.