Basic component of a computer

                           tosinrogue!! Blogger 

2.0       Basic Component of Computer:

            2.1       Diagrammatical Representation of Computer

            2.2       Components of computer and their full function

3.0       The system bus

Basic Component of Computer:

A computer is basically defined as a tool or machine used for processing data to give required information. It is capable of:

a. taking input data through the input unit

b. storing the input data in a cd, hard disk or other medium

c. processing it at the central processing unit (CPU) and

d. giving out the result on the output unit

Fig. 2.1: Representation of a computer

Data: The term data is referred to facts about a person, object or place e.g. name, age, etc.

Information: Is referred to as processed data or a meaningful statement e.g. examination results of students

2.2 Components of computer and their function

The computer system consists of three units:

1. Input device

2. Central Processing Unit (CPU)

3. Output device

Fig. 2.2            Block diagram of a Computer:

1. Input device: Reads information from input media and enters it to the computer in a coded form

2. CPU

(a) Memory unit: Stores program and data

(b) Arithmetic Logic unit: Performs arithmetic and logical functions

(c) Control Unit: Interprets program instructions and controls the input and output devices

3. Output device: decodes information and presents it to the user

Central Processing Unit:

It is the part of the computer that carries out the instructions of a computer program. It is the unit that reads and executes program instructions. Hence it is known as the―brain of the computer. The CPU consists of storage or memory unit, Arithmetic Logic Unit (ALU) and control unit.

(a). Memory Unit: It is also known as the primary storage or main memory. It stores data, program instructions, and results.

(b) Arithmetic and Logical Unit (ALU): It is the unit where all Arithmetic operations (addition, subtraction etc.) and logical functions such as true or false are performed.

 (c).Control Unit: It acts as a central nervous system and ensures that the information is stored correctly and the program instructions are followed in proper sequence as well as the data are selected from the memory as necessary. It also coordinates all the input and output devices of a system

Input Devices

Devices used to provide data and instructions to the computer are called Input devices.

Examples are input devices are:

Keyboard, Mouse, Scanner, Web camera etc.

2.3 Keyboard &Mouse

Output devices

Any device that is capable of representing information on a computer is called an Output device.

Output devices receive information from the CPU and present it to the user in the desired form.

 Output devices are: Monitor, Printer etc.

MEMORY OF THE COMPUTER

Memory or storage capacity is one of the important components of a computer. Any storage unit of a computer system is classified on the basis of the following criteria:

1. Access time: This is the time required to locate and retrieve stored data from the storage unit in response to program instructions.

2. Storage capacity: It is the amount of data that can be stored in the storage unit.

3. Cost per bit of storage.

Units of memory: The computer stores a character in the storage cells with binary (0,1) mechanism.

Thus the basic unit of memory is a bit (binary digit – 0,1). To store a character, a computer requires 8 bits or 1 byte. This is called the ― word length of the storage unit. Hence the storage capacity of the computer is measured in the number of words it can store and is expressed in terms of bytes.

Types of Memory: A computer memory is of two types

1. Primary Memory (Internal storage)

2. Secondary Memory (External storage)

Primary Memory: Primary memory is also called internal memory and is an important part of a computer. It is the main area in a computer where the data is stored. The stored data can be recalled instantly and correctly whenever desired. This memory can be quickly accessed by the CPU for reading or storing information. Primary memory is further classified into two types:

Random Access Memory (RAM) and Read- Only Memory (ROM)

RAM:

RAM is also known as read/write memory as information can be read from and written onto it. RAM is a place in a computer that holds instructions for the computer, its programs and the data. The CPU can directly access the data from RAM almost immediately. However, the storage of data and instructions in RAM is temporary, till the time the computer is running. It is removed from RAM as soon as the power to the computer is switched off. i.e it is volatile memory.

fig. 2.4 RAM

ROM:

It is called Read-only memory as information can only be read from and not written or changed onto ROM. ROM is the ‗built-in memory of a computer. It stores some basic input – output instructions put by the manufacturer to operate the computer. The storage of data and instructions in ROM is permanent.

It does not depend on the power supply. i.e it is non-volatile memory.

Secondary memory: The primary memory which is faster (and hence expensive) is generally not sufficient for large storage of data. As a result, additional memory, called the ―auxiliary or ―secondary memory is used. It is also referred as ―backup storage as it is used to store large volume of data on a permanent basis which can be transferred to the primary memory whenever required for processing.

Some of the devices of secondary storages are Floppy Disk, Hard Disk, CD-ROM, DVD and Flashdrive.

3.0       System Bus

In isolation, the CPU, the memory and the input/output ports are interesting components, but they cannot do anything useful. In combination, they can form a complete system if they can communicate with each other. This communication is accomplished over bundles of signal wires (known as buses) that connect the parts of the system together.

A bus is a communication pathway connecting two or more devices. Multiple devices can be connected to the same bus at the same time. Typically, a bus consists of multiple communication pathways, or lines. Each line is capable of transmitting signals representing binary 1 or binary 0. A bus that connects major computer components (processor, memory, I/O) is called a system bus.

Connecting these parts are three sets of parallel lines which are the address bus, the data bus, and the control bus

 fig. 3.1System Bus

Control Bus

The control bus is used by the CPU to direct and monitor the actions of the other functional areas of the computer. It is used to transmit a variety of individual signals (read, write, interrupt, acknowledge etc) necessary to control and coordinate the operations of the computer. The individual signals transmitted over the control bus and their functions are covered in the appropriate functional area description.

Address Bus

The address bus consists of all the signals necessary to define any of the possible memory address locations within the computer, or for modular memories any of the possible memory address locations within a module. An address is defined as a label, symbol, or other set of characters used to designate a location or register where information is stored. Before data or instructions can be written into or read from memory by the CPU or I/O sections, an address must be transmitted to memory over the address bus.

Data Bus

The bidirectional data bus, sometimes called the memory bus, handles the transfer of all data and instructions between functional areas of the computer. The bidirectional data bus can only transmit in one direction at a time. The data bus is used to transfer instructions from memory to the CPU for execution. It carries data (operands) to and from the CPU and memory as required by instruction translation. The data bus is also used to transfer data between memory and the I/O section during input/output operations.

Today all computers utilize two types of buses, an internal bus and an external bus. An internal bus enables a communication between internal components such as a computer video card and memory (e.g. ISA, EISA, PCI, AGP, etc.) and an external bus is capable of communicating with external components such as a SCSI bus, GPIB, etc.

Fig. 3.2 Internal and External