Functions of CPU, Memory and Input /Output Devices

        CENTRAL PROCESSING UNIT (FUNCTIONAL PARTS AND FUNCTIONS)

The central processing unit comes in action when the input has been recorded through input unit. The central processing unit is responsible for actual processing of inputs to generate the output. The central processing unit (CPU) is considered as the brain of the computer. It is also called as Microprocessor. This device converts all the supplied input into output as per the instructions supplied by the user. The CPU of a computer is the device on which the speed and efficiency of the computer mainly depends on.

Fig. 1.3 : Central Processing Unit

The CPU is divided into arithmetical & logical unit (ALU) and Control Unit (CU). The ALU performs arithmetical and logical calculations and CU supervises the working of ALU.

Computer cabinet is not CPU. CPU is fitted inside it.

(a) Control Unit: The control unit acts as supervisor on the working of ALU. At a time, there are many programs to be executed by CPU. They must be executed in a proper sequence. This sequence is decided by CU. The control unit takes instructions stored in memory and issues signals to ALU depending on these instructions. It also coordinates the functioning of various input output devices attached to computer.

(b)Arithmetic and Logic Unit: The arithmetic and logical unit is the part of CPU where actual computation is performed. It is the place where all the arithmetical calculations and logical comparisons are performed. The arithmetical calculations involve the use of basic arithmetic operations like addition and subtractions.

The logical calculations involves checking numbers and letters for equality, less than and greater than conditions. The other conditions that can be tester are greater than or equal to, less than or equal to and not equal to. These calculations are performed on data that is stored in internal storage areas of CPU, called registers.

The actual processing of data occurs in the ALU.

(c) Registers: Registers are internal storage locations inside the CPU that are used to store instructions or data. The registers are used by ALU and CU for storing intermediate results and control information. Different models of CPU are different in number and size of registers. As these locations are internal to CPU, they can be rapidly accessed by it. There are many types of registers.

        ·  The Program Counter is used to keep the address of the next instruction to be fetched.
        ·  The Instruction Register is used to store the address of the current instruction    
             that is being processed.
        ·  The Address Registers are used by instructions for indirectly accessing the
             contents of memory by its address.

   MEMORY

The memory unit is one of the most important sections of computer. It is responsible for storing the data and instructions either temporarily or permanently. This is the section due to which the computer can store and remember thousands of different files of various types. The memory is the storage area where all the inputs are stored before processing and the outputs are stored after processing of inputs. Many devices provide input to computer and a space is required to store and queue all these inputs, before they are processed by the CPU. This is because these inputs are to be processed one by one.

Similarly, when the CPU processes the inputs to produce outputs, there must be a space where these outputs could be queued up. The memory serves as the space to store the instructions. If the output device is busy in producing an output, the other outputs are queued up in the memory.We would be discussing various types of memories and memory devices in the following pages of this chapter. We will also talk about the properties of these devices. You will come across many new words and technologies. The most important for all this understanding is to know about the units of memory. You can understand the capacity of a memory device only if you understand the units of memory

Units of Memory

We use various units to measure various types of materials. You know that the liquids are measured in litres and the solids are measured in kilograms. Similarly, we have units to measure the volume of memories of a computer.

Following are the units of memory:
·  1 bit: It is the space required to store one binary digit (0 or 1) in the memory.

· 1 byte: It is the space required to store one character of the keyboard into the memory. It is equal to 8 bits. One character (“a” or “b” or “c” …) takes 8 bits to get stored in memory. All the symbols or numbers also take the same space when stored as text in the memory.

·  1 Kilobyte (KB): 1 Kilobyte is the space required to store 1024 bytes in the memory. Therefore, 1 KB=1024 bytes

·  1 Megabyte (MB): One Mega Byte is the space required to store 1024 kilobytes in memory. Therefore, 1MB= 1024 x 1024 bytes.

·  1 Gigabyte (GB): One GB is the space required to store 1024 megabytes in the memory. Therefore, 1GB= 1024 x 1024 x 1024 bytes

·  1 Terra Byte (TB): One Terra Byte is the space required to store 1024 GB in the memory. Therefore, 1Tb= 1024 × 1024 × 1024 × 1024 bytes.

       Functions of Memory

The data and instructions that are entered into the computer system through input units have to be stored inside the computer before actual processing starts. Also the results produced after processing must be kept somewhere inside the computer before being passed on to the output unit. Moreover the intermediate results produced by the computer must also be preserved for on-going procession. The memory of a computer system is designed to cater all these needs. It provides space for storing instructions and data, space for intermediate results and space for final results.

The functions of memory are as follows :

(i)  Stores the data and instructions to be processed.

(ii) Stores intermediate results of processing.

(iii)Stores the final results of processing before these are released to an output device.

       FUNCTIONS OF INPUT/OUTPUT DEVICES

Input Devices

Data and instructions must enter a computer system before the computer can perform any computation on the supplied data. The input unit that links a computer with its external environment performs this task. Data and instructions enter a computer through an input unit in a form that depends upon the input device used. For example, data can be entered using a keyboard in a manner similar to typing and this differs from the way in which data is entered through a scanner, another type of input device. However, a computer's memory is designed to accept input in binary code and hence, all input devices must transform input signals to binary codes. Units called input interfaces accomplish this transformation. Input interfaces match the unique physical or electrical characteristics of input devices to the requirements of a computer system.

In short, an input unit performs following functions:

1.  It accepts (or reads) instructions and data from outside world.

2. It converts these instructions and data in computer acceptable form

3. It supplies the converted instructions and data to computer system for further processing.

Various Input Devices are:

·           Keyboard

·           Mouse

·           Magnetic Ink Character Reader (MICR)

·           Optical Mark Reader (OMR)

·           Track ball

·           Touch Screen

·           Light Pen

·           Card Readers

·           Scanners

·           Joystick etc.

  Output Devices

An output unit performs the reverse operation of that of an input unit. It supplies information obtained from data processing to outside world. Hence, it links a computer with its external environment. As computers work with binary code, results produced are also in binary form. Therefore, before supplying the results to outside world, the system must convert them to human acceptable (readable) form. Units called output interfaces accomplish this task. Output interfaces match the unique physical or electrical characteristics of output devices (terminals, printers, etc.) to the requirements of an external environment.

In short, an output unit performs following functions:

1.It accepts the results produced by a computer, which are in coded form and hence, we cannot         easily understand them.

2.It converts these coded results to human acceptable (readable) form

3.It supplies the converted results to outside world. There are two broad categories of outputs from            computers.

1.         Soft Copy Output

2.         Hard Copy Output

(i) Soft Copy Output: Soft copy output is the temporary form of output that can be seen till the computer is powered on. This output is not available when the computer is powered off. For example, the data displayed on the screen of our monitor is available till the computer is switched on and the songs can be heard from speakers till the computer is powered on.

(ii)Hard Copy Output: We cannot only work with soft copy output. Such output is temporary and we need output for record keeping purpose also. For example, a receipt of the payment is required for customer as well as for internal records. That is why we need hard copy output on paper. This type of output is printed on paper and can be referred at any point of time. Hard copy output is the permanent type of output that can be referred at any point of time. For example, you can see the printed sales report of the month even when your computer is switched off.

Various output devices are

*           Monitor

*           Printer

*           Plotter

*           Speaker