Computer Notes | Computer Basics | Input Units | CPU | Components of CPU | Instruction Cycle (Fetch Execute Cycle) | Control Unit and Function of Control Unit | GIGO (Garbage In Garbage Out)
Computer System
A group of equipment put together to process data is called a computer system. A computer system consists of several components to achieve electronic data processing.
1. Input Units
They are devices which accept data from user and transmit it to the central processing unit as electronic pulses. For example, the ATM (Automatic teller Machine) system, when we want to withdraw, we are required to enter our Personal identification number (PIN). When we enter our PIN, we are using an input device, the keypad.
2. CPU (Central Processing Unit)
It is an abbreviation for central processing unit and is pronounced as separate letters. The Central Processing Unit is the brain of the computer sometimes referred to simply as the central processor, but commonly called processor. The Central Processing Unit is the unit where most calculations take place. It is linked with the input units and output units to form the computer system. In terms of computing power, the CPU is the most important component of a computer system. On the personal computer (PC) and small workstations, the CPU is housed in a single chip called a microprocessor or microchip.
The fundamental sequence of steps that a CPU performs is also known as the fetch-execute cycle or instruction cycle. It is the time in which a single instruction is retrieved from memory, decoded (determined what actions the instruction requires), and executed (carried out those actions). The first half of the cycle transfers instruction from memory to the Instruction register and decodes it. The second half executes the instruction. This cycle is repeated continuously by the CPU from Start or boot-up to the time when the computer is shut down.
Instruction Cycle (Fetch Execute Cycle)
Each computer’s CPU can have different cycles based on different instruction sets, but will be similar to the following cycle-
1. Fetch the Instruction
The CPU fetches the instruction from the main memory via the data bus, and it is then placed into the CIR (current instruction register). The Program Counter is instructed to contain the address of the next instruction.
2. Decode the Instruction
The instruction decoder interprets instructions. If an instruction has an indirect address, the effective address is read from the main memory, and any required data is fetched from the main memory to be processed and then placed into data registers.
3. Execute the Instruction
The CU passes the decoded information as a sequence of control signals to the relevant functional units of the CPU to perform the actions required by the instruction, such as reading values from registers, passing them to the ALU to perform mathematical or logic functions on them, and writing the result back into a register. If the ALU is involved, it sends a condition signal back to the CU.
4. Store Results
The result generated by the operation is stored in the main memory, or sent to an output device. Based on the condition of any feedback from the ALU, Program Counter may be updated to a different address from which the next instruction will be fetched. The cycle is then repeated.
There are Two Main Components of a CPU
A. The Arithmetic Logic Unit (ALU)
It performs all arithmetic operations and decision-making operations.
1. Data Transfer
It includes moving data from one location to another within the computer.
2. Arithmetic Operation
It includes addition, subtraction, multiplication, division, etc.
3. Decision Making
It is an ability to compare two quantities and perform logical operations such as compare, true or false, etc.
B. The Control Unit (CU)
It extracts instructions from memory and decodes and executes them, calling on the ALU, when necessary. It controls all functions and coordinates all components of the computer. It is in charge of the fetch-execution cycle.
Functions of the Control Unit
1. Control Flow of Data
- From input devices to memory
- From memory to output devices or secondary storage
- From secondary storage to memory
- From ALU to memory
- From memory to ALU
2. Co-ordinates Instructions Execution
- Fetch the instruction
- Decode the instruction
- Execute the instruction
More components of a CPU, that are vital to its operation, are the registers which are very small memory locations that are responsible for holding the data that is to be processed.
3. Output Units
Devices which accept information from the CPU and convert it to a human-readable form. For example, when we pay the cashier in the supermarket, he will give a receipt. This receipt is a form of output from the output device known as the printer.
GIGO (Garbage In Garbage Out)
It is a concept of computer science that the quality of output is determined by the quality of input, means wrong input will result in wrong output. It is related to the accuracy of input and output.
What is ATM?
The full form of ATM is Automatic Teller Machine. We can make cash withdrawals without staff from it.
Which is a part of the CPU?
ALU is a part of the CPU.
What is the full form of EDP?
The full form of EDP is Electronic Data Processing.
What is the full form of CPU?
The full form of CPU is Central Processing Unit.
What is the full form of ALU?
The full form of ALU is Arithmetic Logic Unit.