What is Center Processing Unit (CPU) and It's Components & how to work?

What is CPU?

How the components of computer work?

CPU stands for “Central processing unit”. The part of a computer in which operations are controlled and executed is called CPU.

It is also known as microprocessor or processor. A CPU is brain of a computer. It is responsible for all functions and processes. Regarding computing power.

The CPU is the most important element of a computer system. The CPU is consisted of thin layers of thousands of transistors. Each transistor receives a set of inputs and produces output. Transistors hold a key role in functioning of CPU as they make computer able to count and perform logical operations which is called processing. It processes the instructions that it collects by decoding the code in programs.

Computers use two types of storage:

Primary storage

Secondary storage

The CPU mainly interacts with primary storage or main memory, referring to it for both instructions and data. 

 There are four important functions of CPU:

• Fetch
• Decode
• Execute
• Write back

Main Components of CPU:

The main components of CPU help it in performing various functions. The components of a CPU work together, and their making/manufacturing determine the complexity of operations as well as how fast they can be carried out.

The three components of the CPU are following:

1. Arithmetic Logic Unit
2. Control Unit
3. Registers

Arithmetic Logic Unit (ALU):

There is electronic circuitry in arithmetic logic unit which executes all arithmetic and logical operations. Its function is obvious from its name. It performs arithmetic calculations like as addition, subtraction, multiplication and division as well as comparisons. The unit can compare numbers, letters, or special characters. There can be more than one Arithmetic logic unit in a CPU, and these ALU system can also be used for the purpose of maintaining timers that help run the computer.


Control Unit(CU):

There is circuitry in the control unit which uses electrical signals to instruct the whole computer system for carrying out or executing, already stored program instructions. Its name clearly shows that it controls and co-ordinates computer components. It extracts instructions from memory and decodes and executes them. In fact it regulates the flow of information through the processor. In short, it can be said, this component receives, decodes, stores results and manages execution of data that flows through the CPU. Its communication with both arithmetic unit and memory is inevitable.

Registers/The Memory Unit:

1. Registers are temporary storage areas which are responsible for holding the data that is to be processed. They store the instructions and data in a processor. This data is further used by Control Unit. There are some registers that are set aside for specific tasks, these generally include a program counter, stack, and flags.

2. A CPU register is a special memory location constructed from flip-flops that do not form part of the memory and are used for arithmetic and location operations. They are usually addressed by other mechanisms than the main memory and can be accessed more quickly. 

Mostly used Registers named:

• Accumulator Register (AC)
• Data Register (DR)
• Memory Address Register (MAR)
• Program counter (PC)
• Memory Data Register (MDR)
• Index Register (IR)
• Memory Buffer Register

Explanation of Registers types.

Accumulator Register (AC):

This Register is used for storing the Results those are produced by the System. When the CPU will generate Some Results after the Processing then all the Results will be Stored into the AC Register.

 

Data Register (DR):

A register used in microcomputers to temporarily store data being transmitted to or from a peripheral device.

Memory Address Register (MAR):

MAR stand for Memory Address Register. This register holds the memory addresses of data and instructions. This register is used to access data and instructions from memory during the execution phase of an instruction. Suppose CPU wants to store some data in the memory or to read the data from the memory. It places the address of the-required memory location in the MAR.

 

Program Counter (PC):

The program counter (PC), commonly called the instruction pointer (IP) in Intel x86 microprocessors, and sometimes called the instruction address register, or just part of the instruction sequencer in some computers, is a processor register

It is a 16 bit special function register in the 8085 microprocessor. It keeps track of the the next memory address of the instruction that is to be executed once the execution of the current instruction is completed. In other words, it holds the address of the memory location of the next instruction when the current instruction is executed by the microprocessor.

Memory Data Register (MDR):

MDR is the register of a computer's control unit that contains the data to be stored in the computer storage (e.g. RAM), or the data after a fetch from the computer storage. It acts like a buffer and holds anything that is copied from the memory ready for the processor to use it. MDR hold the information before it goes to the decoder.

  MDR which contains the data to be written into or readout of the addressed location. For example, to retrieve the contents of cell 123, we would load the value 123 (in binary, of course) into the MAR and perform a fetch operation. When the operation is done, a copy of the contents of cell 123 would be in the MDR. To store the value 98 into cell 4, we load a 4 into the MAR and a 98 into the MDR and perform a store. When the operation is completed the contents of cell 4 will have been set to 98, by discarding whatever was there previously.

  The MDR is a two-way register. When data is fetched from memory and placed into the MDR, it is written to in one direction. When there is a write instruction, the data to be written is placed into the MDR from another CPU register, which then puts the data into memory.

  The Memory Data Register is half of a minimal interface between a micro program and computer storage, the other half is a memory address register.

 Index Register (IR):

A hardware element which holds a number that can be added to (or, in some cases, subtracted from) the address portion of a computer instruction to form an effective address. Also known as base register. An index register in a computer's CPU is a processor register used for modifying operand addresses during the run of a program.

Memory Buffer Register:

  MBR stand for Memory Buffer Register. This register holds the contents of data or instruction read from, or written in memory. It means that this register is used to store data/instruction coming from the memory or going to the memory.