BASIC OPERATIONS BY BASIC UNITS
These three basic units correspond to the five basic operations performed by the computer system.1. Input Unit
2. Output Unit
3. Processing Unit
i. Memory Unit
ii. Arithmetic Logic Unit
iii. Control Unit
Following is a block diagram of the organization of basic computer units; in this figure the solid lines are used to indicate the flow of instruction and data, and the dotted lines represent the control exercised by the control unit. It displays the five major building blocks, or functional units of a digital computer system.
INPUT UNIT
Input unit can be defines as:
“Unit which is used to get data from the user to computer is called the input unit”
The input unit receives the input of data which is in need of processing. For this purpose different input devices (i.e. keyboard, mouse etc) can be used. These devices are helpful to make connection between the outer environment and the inner environment of the computer. The data provided by the input devices to the computer is transformed into the binary codes which are acceptable by the computer memory.
Following are the functions performed by the input unit:
1. It accepts (or reads) the list of instructions and data from the outside world of computer.
2. It converts these instructions and data in computer acceptable form.
3. It supplies the converted instructions and data to the computer system for further processing.
CENTRAL PROCESSING UNIT (CPU)
Central processing unit can be defined as:
“The computer‟s brain which organizes and carries out instructions from either the user or the software”
CPU resides on a circuit board called the motherboard and can be described as the "brains" of the computer. The control unit (CU), memory unit (MU) and the arithmetic logic unit (ALU) of a computer system are jointly known as the “central processing unit (CPU)”. The CPU is the brain of any computer system. In a human body, all decisions are taken by the brain and the other parts of the body function as directed by the brain. Similarly, in a computer system, all calculations and comparisons are made by or inside the CPU and the CPU is also responsible for activating and controlling the operations of other units of computer system.
FUNCTIONS OF CENTRAL PROCESSING UNIT (CPU)
CPU performs the following main functions:
1. Fetch (read) data and programme instructions
2. Decode them
3. Execute them
4. Control the flow of program and date in and out of RAM
5. Place results of processing in memory
PARTS OF CENTRAL PROCESSING UNIT (CPU)
1. Arithmetic and Logic Unit (ALU)
2. Memory Unit (MU)
3. Control Unit (CU)
MEMORY UNIT (MU)
The memory unit of CPU is the place where the computer program and data are stored during processing. It is a random access storage device consisting of thousands upon thousands of storage locations, each of which can be directly reached by the control unit. Each storage location is distinguished by a unique number called its Address. During a processing procedure, different data may be stored in any given storage location, but the address of the storage location is fixed. For example: the memory unit is often compared to a post office. At various times different letters are placed in a postal box, but the box number is always the same. Following are the basic functions performed by the memory unit:
1. Having all the data to be processed and the instructions required for processing (received from input devices).
2. Having intermediate results of processing.
3. Having final results of processing before these results are released to an output device
ARITHMETIC LOGIC UNIT (ALU)
The arithmetic logic unit (ALU) of a computer system is the place where the actual execution of the instructions takes place during the processing operation. All calculations are performed and all comparisons (decisions) are made in ALU. Data stored in primary storage before processing, transferred as and when needed to ALU where processing take place. After processing data transferred to primary storage, so data may move from primary storage to ALU and back again to storage many times before processing is over. After the completion of processing, the final results which are stored in the storage unit are released to an output unit.
Following are the basic functions performed by the arithmetic and logic unit:
1. It performs arithmetic processing like addition, subtraction, multiplication and division.
2. It performs logical processing like less than, greater than, equal to etc.
CONTROL UNIT (CU)
It is the control unit who tell the input unit that it is time for it to feed data into the memory unit. It also handles ALU to tell what should be done with the data when it receives it. Control unit is also responsible to send only the final results to output device not the intermediate results. It is the responsibility of control unit to maintain order and direct the operation of the entire system. Although, it does not perform any actual processing on the data, the control unit acts as a central nervous system for the other components of the computer. It manages and coordinates the entire computer system. It obtains instructions from the program stored in main memory (RAM), translate the instructions, and issues signals that cause other units of the system to execute them.
Following are the basic functions performed by the control unit:
1. It controls all the units or parts of computer system directly or indirectly.
2. Directly control to ALU and MU. 3. Indirectly control to input and output units.
OUTPUT UNIT
Output unit can be defined as:
“Unit which is used to get data from the computer to user is called the output unit”
This unit supplies information and results of computation to the outside world. Thus it links the computer with the external environment. As the results are in the binary form, so the conversion of these binary codes to user understandable form is the responsibility of output devices (i.e. monitor, printer etc.) Following are the functions performed by the output unit:
1. It accepts the results produced by the computer which are in coded form and hence cannot be easily understood by us.
2. It converts these coded results to human acceptable(readable) form,
3. It supplies the converted results to the outside world.
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