Central Processing Unit

Central Processing Unit

CPU Components | CPU Registers | CPU Computer

CPU Architecture | CPU Comparison

The Central Processing Unit ( CPU )  is the brain of the Computer System . The CPU is also alternately referred as a Computer Processor  Or Microprocessor or simply a processor. The microprocessor is one the most crucial component that provides the processing power to the computer system.

The CPU initiates the program execution by fetching the program instructions and the data to be operated from the main memory RAM.

How To Install Processor CPU On The Motherboard , CPU , Microprocessor , Processor , Central Processing Unit

The Central Processing Unit (CPU) is a fundamental component of a computer system and is often referred to as the “brain” of the computer. It performs most of the processing operations inside a computer, executing instructions and managing data manipulation. The CPU interprets and executes instructions from the computer’s memory, coordinating the activities of all the hardware components to perform various tasks.

Different types of CPUs exist, including those designed for personal computers, servers, mobile devices, and specialized applications like graphics processing units (GPUs). The performance of a CPU is influenced by factors like architecture, clock speed, cache size, and the number of cores. As technology advances, CPUs continue to evolve, becoming faster, more efficient, and capable of handling increasingly complex tasks.

In this article, we will learn what is a processor , functions Of the CPU , How CPU executes the computer program instructions , machine cycle , instruction cycle and other related important topics.

What Is Central Processing Unit ?

The CPU stands for  Central  Processing  Unit  of  the Computer System. The CPU  is also alternately referred to as a processor, central processor , or  a  microprocessor

 The  CPU is the  brain of the computer where all  arithmetic  calculations  and  logical  operations  take  place. A computer’s CPU handles all the  instructions it receives from  computer hardware  and  the software applications  running  on the  computer  system .

Intel Processor , Central Processing Unit
Processor Is System Brain

The processor ( CPU ) controls all the activities of the computer system. And therefore, it is referred as brain of the computer system.

There are two main computer processor manufacturers  Intel and Advanced Micro Devices ( AMD ). These two companies produce most of the processors used in desktop,  laptops  and  notebooks.

A   CPU  is  placed  on  the  motherboard  in  a  processor  socket  with  locking  liver mechanism   in  order  to  fix  the  processor  chip  properly  into the  processor  socket . The processor socket contains a IC socket in which the processor  chip is firmly mounted .

A heat-sink  is mounted on the top of the processor chip which  protects  the processor chip from the excessive  heat generated.

Processor Socket On Mother Board , Central Processing Unit

The Computer System  consist of four major units and that includes :

  1. Input Unit  2. Output Unit   3.  Memory  Unit  4.  Central  Processing Unit  ( CPU ).
Computer System Block Diagram , Central Processing Unit

The main function of the input unit is to allow the system user to input the data that needs to be processed with the help of application software . It is also alternately referred to as the program data,

Some of the standard user input devices ( peripheral devices ) include a keyboard , mouse , scanner , camera and other such input devices.

Computer Input Devices
Computer Output Devices

The main function of the output unit is to present the information ( processed data ) to the system user in the desired format. The data after being processed by the CPU is sent to the main memory RAM . The operating system then sends this data to a specific output device as per the program instruction.

The data after CPU operation is also alternately referred to as the processed data. The user might want to either display the program output or store the data in any permanent storage device such as disk memory.

Some of the standard user output devices ( peripheral devices ) include a display monitor , printer , projector, speaker , storage disk and other such output devices.

Functions Of Central Processing Unit

The CPU performs some of the most important functions in a computer System . The most important function for the CPU is to continuously  perform Instruction Cycle. The CPU  executes a program by repetitively performing the instruction  cycle. 

The Instruction cycle basically consist of four operations . These four operations include 1. Fetch 2. Decode 3. Execute 4. Store  .These four operations are sequentially and continuously performed by the CPU during the program execution.

Central Processing Unit

CPU Functions

  • To perform Arithmetic calculation operations.
  • To perform logical operations.
  • To control functions of other hardware components..
  • To fetch the data and program instructions from main memory RAM.
  • To decode the program instructions.
  •  To operate on the data as per program instructions.
  • To store the processed data into the RAM.
  • To continuously execute instruction / machine cycle.
  1. Instruction Execution: The CPU fetches instructions from memory, decodes them to understand their meaning, and then executes them by performing calculations, data manipulations, or controlling other hardware components.
  2. Arithmetic and Logic Operations: The CPU performs arithmetic calculations (addition, subtraction, multiplication, division) and logic operations (AND, OR, NOT) to process data and make decisions.
  3. Control Unit: This part of the CPU manages the order of operations and controls the flow of data between different parts of the computer system. It coordinates the execution of instructions and ensures they are executed in the correct sequence.
  4. Registers: These are small, high-speed storage locations within the CPU that hold data temporarily during processing. Registers store data that is being actively worked on, helping to speed up calculations and operations.
  5. Clock Speed: The CPU operates at a specific clock speed, measured in Hertz (Hz), which determines how many instructions it can execute per second. Higher clock speeds generally result in faster processing, although other factors like architecture and efficiency also play a role.
  6. Cores: Many modern CPUs have multiple processing cores, allowing them to execute multiple tasks simultaneously. These cores can work independently or in coordination, improving multitasking and overall system performance.
  7. Cache Memory: The CPU often includes different levels of cache memory that store frequently used data and instructions. Cache memory is faster to access than main memory (RAM), which helps reduce the time the CPU spends waiting for data.
  8. Pipeline Processing: CPUs often use pipelines to process multiple instructions simultaneously. Each instruction goes through stages of fetching, decoding, executing, and storing results, allowing the CPU to work on different parts of multiple instructions at the same time.
  9. Floating-Point Unit (FPU): The FPU is responsible for handling floating-point arithmetic operations, which are used in complex calculations involving decimal numbers and real numbers.

Central Processing Unit

CPU Functions

The CPU performs some of the most important functions within a computer system. These functions include :

  •   Fetching the program instructions from main system memory RAM one by one and starts its execution.
  • To control the functioning of other hardware components by sending and receiving control signals on the control buses.
  • To decode and operate on the program data as per program instructions and perform arithmetic and logical operations.
  • To send the processed data back to the main memory RAM  that can be stored in permanent memory ( disk memory ) .
  • To repetitively perform machine cycle during the program execution.

CPU Components

Components Of Central Processing Unit

The  CPU  is  primarily  responsible to do all the calculations  , Logical Operations such as decision making  and controlling other hardware components and devices connected to the computer  system . 

The CPU  is  a  single microprocessor chip which  performs  all  these functions . The CPU chip internally can be grouped into three major units as per their function. The main  internal  CPU components include  1. ALU  –  Arithmetic  Logic  Unit  , 2. CU   –  Control Unit  and  3. Memory  Unit .

1. Control Unit ( CU ).

2. Arithmetic Logic Unit ( ALU ).

3. Memory Unit ( MU ) .

Control Unit

The control unit ( CU ) is one of the  internal component of a computer’s central processing unit ( CPU ). The Control Unit  directs all  the operations  of  the  processor . The control unit  directs the computer’s memory , arithmetic and  logic unit , input and output devices.  It is the control unit that decides on  how to respond  to  the program’s instructions  during  the program  execution.

Central Processing Unit Components
Instruction cycle , Microprocessor , CPU , Processor

How CPU Control Unit Works ?

The control  unit ( CU ) directs  the  operation  of the other units   by  providing  timing  and  control  signals to synchronize their operations .    

The  control unit  is  typically  an  internal  part of the CPU  with  its  overall  role  and  operation  unchanged  since  its  introduction .  Most  of the computer  resources  are  managed  by the control unit .

The control unit  also  directs   the   flow  of  data  between the   CPU  and  the  other devices especially the data flow between main memory RAM and the CPU.

The control unit  decodes and translates  the program machine code  instructions during the program execution. The control unit then generates the necessary  signals  for  Arithmetic Logic Unit ( ALU )  and  for other units to perform the desired operation on the data. 

All the operations of the computer system are synchronized  by steam of clock pulses generated by the CPU  clock .  This   timing   signals  generated  by  the     CPU clock are generated by the control  unit which  synchronizes  all the  activities and different  operations.

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What Is CPU Control Unit ?

What Is ALU ?

Arithmetic Logic Unit ( ALU )

The ALU stands for  Arithmetic Logic Unit . It is another  complex digital circuit  that is part of every processor and one of many components within a computer’s central processing unit .  

The ALU  performs both bit-wise logical and mathematical operations  on the binary numbers. The ALU   is  the  last component to perform the arithmetic calculations and logical operations in the processor.

Arithmetic Logic Unit , Central Processing Unit , What IS CPU , Instruction Cycle

The ALU  operates on the data as per the program instruction decoded by the control unit of the CPU. And therefore , the data is actually processed by the ALU in terms of CPU operations.

The processed data is then sent to the main memory for further action. The operating system can either sent this data to the output unit such as monitor or it can sent to any permanent storage device for future use. 

CPU Memory Unit

The Memory Unit ( MU )  inside the CPU consist of two components and that includes CPU Registers and  Cache Memory ( L1 ) .

In order to optimize the CPU performance , the CPU needs high speed memory area to store the frequently used data during the program execution.

The CPU makes use of its very high speed memory registers during the various stages of the machine cycle. These registers are the fastest memory in the memory hierarchy.

CPU Registers

Each CPU contains number of  high speed memory  registers .During the program execution , CPU makes use of its internal memory  registers  .

These registers are used by the processor as  a  high speed  temporary storage  memory area during the  various stages of execution of  the instruction cycle . The  CPU  can directly   access  these  registers  to  perform   the desired operation   on  the  data.

Cache Memory ( L1 )

In addition to CPU Registers , the CPU also contains   Level 1 Cache memory . The L1 Cache is used by CPU  to store the frequently used  data  and  instruction  during the program execution

Cache Memory Levels ( L1 , L2 , L3 )

Cache Memory

Central Processing Unit

Machine Cycle

Instruction Cycle , Processor Cycle

The  Computer  programs  are  written  to  solve  some  specific  problems. A computer  program  directs the computer CPU  to  perform  specific operations  on the  data  and  produce the desired  output that can be used for some meaningful work.

The computer programs are generally written in a human readable  programming languages such as C , C++ , Java , Python.

The program written in any programming language  needs to be first converted  into machine readable  program instructions  in BINARY ( Machine Code )  that  can be directly  executed  by the computers CPU – Central Processing Unit.

The process to convert program written in high level language into machine readable binary code is referred as program compilation.

Central Processing Unit

What Is Machine Cycle ?

The CPU is the main component in a computer system  , which is  responsible  to  interpret  and execute  the program instructions .

The CPU  executes a program by repetitively performing a sequence of operations ( Fetch , Decode , Execute And Store )  which is collectively referred as Instruction Cycle.

The machine cycle refers to the one part of the instruction cycle.

A instruction Cycle ( Also referred as machine Cycle Or Processor Cycle )  is the basic operation performed by the  CPU – Central Processing Unit to execute a program.

The CPU  can  execute  the program instruction either  in a single  machine cycle  or  multiple  machine cycles.   Depending  upon the  complexity  of  the  instruction , the CPU can take more than one machine cycles to execute one instruction. This is called instruction cycle. 

Learn More About Machine Cycle

What Is Instruction Cycle ?

Although a machine cycle is also referred as Instruction Cycle but there two CPU operations are a bit different.

The instruction cycle is the time taken by the CPU to execute one instruction which include fetch , decode and execute operation.

The processor  can  execute  one single instruction either  in a one  machine cycle  or CPU might need more than one  machine cycles which  depends  upon the  complexity  of  the  instruction. 

Learn More 

What Is Instruction Cycle ?

How CPU Works ?

The CPU is responsible to execute the program . The Operating system allocates the necessary resources in terms of memory required and the processor time . The Operating system loads the program into the main  memory  RAM.

The CPU now starts the program execution . During the program execution , the CPU makes use of internal high speed  memory of the CPU which includes L1 Cache memory and the CPU Registers .

Computer System Memory Hierarchy

The CPU initiates the program execution by loading the address of the first instruction in to the PC register. 

The program instruction consist of two parts that is OP Code ( Operation Code And the data ( operand ) on which needs to be processed . The This address is then transferred to MAR ( Memory Address Register ) and PC counter is simultaneously incremented .

How CPU Decodes Program Instructions ?

The CPU fetches the Data and program instruction from the main memory and transfer these to other internal registers ( MBR and IC )  for further processing . 

The control unit of the CPU decodes the program instruction into OP Code  ( Operation code ) and Operand ( Data ) .

Machine Instruction Format

Machine Instruction

Machine Instruction Format

OP Code And Operand

This  data and the OP Code is then transferred to ALU ( Arithmetic Logic Unit ) of the CPU for operation . The ALU operates on the data as per the OP code and the corresponding operation as defined in the ISA ( Instruction Set Architecture ) Of the CPU . 

Once the data is operated by the ALU , the processed data is than set to the main memory RAM . This data is then either sent to any output device Or stored on any secondary storage device ( Hard disk ) for future use .

How CPU Executes Program ?

How CPU Works , Central Processing Unit

Central Processing Unit

Machine Cycle | Instruction Cycle


A machine cycle consists of a sequence of four steps that are performed continuously by the CPU . The CPU performs these steps millions of times per second during all the activities performed by the CPU and also during the program execution.

These steps are  Fetch , Decode Execute And  Store.

During the fourth step, store, in which the result of  the processing done by the CPU  is  stored  into the  main memory ( RAM ). 

This data is either sent output device or stored in secondary storage ( hard disk )  for later use. . However , no actual  processing  is  performed  during  this  step .

Instruction Cycle

CPU Machine Cycle Steps , Central Processing Unit

Machine Cycle Steps

CPU Machine Cycle

Instruction Cycle Steps

The machine cycle is the part of instruction cycle . And therefore , depending upon the type of the instruction , a single instruction might need one or more machine cycles to get executed by the CPU.

The minimum number of machine cycles requited is one and the maximum number of machine cycles is four to execute one instruction.

  •   The Operating System loads the data and program instructions to be executed into the main memory RAM.
  • The CPU initiates the program execution by fetching the data and instruction one by one into the internal memory of the CPU ( Registers ).
  • The control unit then decodes the OPCODE to perform the desired operation . 
  • The CPU then finds the memory address of the operand and retrieves the operand.
  • The ALU performs the desired operation on the operand as per OPCODE. 
  • The CPU locates the address  of the destination memory  ( main memory RAM ).
  • The CPU stores the processed data into the destination memory .
  • The CPU repetitively performs the machine cycle during the program execution.

Central Processing Unit ( CPU )

Instruction Set Architecture

Microprocessor ( ISA )

The Microprocessor within a computer system is responsible to perform a predefined set of operations .

These CPU predefined set of operations include arithmetic operations , logical operations . data transfer operations  and  other operations that defines the computers response to various events ( User Or Program Instructions ) .

Each microprocessor design is based on the set of binary commands and the processor supports these predefined set of instructions . 

This set of commands implemented ( embedded into the processor chip ) by the microprocessor into its micro-architecture is referred as “Instruction Set Architecture” ( ISA ) .

In other words , An  instruction is a binary pattern defined inside a CPU   (  Microprocessor  )   to perform  a  specific  operation .

The  entire  group  of  these binary machine code  instructions  that  is  implemented  and supported  by the  microprocessor  is  called as “Instruction  Set”  . For  Example  ISA  8085  has  246  instructions.

Instruction Set Architecture ?

Instruction Set Architecture

What Is ISA In CPU ?

Microprocessor Instruction Set Architecture

Central Processing Unit Performance

There are several factors that affect the CPU performance. Amongst the most  important factors  which directly  affect  the  CPU  performance  are :

1.  CPU  Speed  And  Design  .

2.  RAM  Size  And  Type .

3. Operating  System  Type  .

Central Processing Unit Performance , Central Processing Unit

CPU Speed

What Is Microprocessor Speed ?

The Microprocessor in a computer system is responsible to perform a predefined set of operations that includes arithmetic operations , logical operations , data transfer operations  and  other operations that defines the computers response to various events ( User Or Program Instructions ) .

The  clock speed  is important measure of  speed of a  processor . The clock speed of a processor is how fast the processor can do the tasks while executing a program. The Clock speed is measured  in  Megahertz ( MHz ) or  Gigahertz ( GHz ).

1 MHz  = One million clock ticks every second.

1 GHz = One billion clock ticks every second.

 This  means  that  if one instruction was carried out per clock tick , a 3GHz processor could execute three billion instructions  for   three  billion  clock ticks  every  second.

Central Processing Unit Speed

CPU Clock Speed

Every  microprocessor  requires a stream of clock pulses ( binary square pulse  )  for its functioning .  The  CPU  requires a fixed number of clock ticks ( called as  Clock cycle / Clock Speed  ) to execute  each  instruction.

A  CPU  is  driven by an internal clock  which generates a stream of square waves that regulates the rate  at which instructions are executed by the CPU  and synchronizes  all  other  components in a computer system.

The faster the clock cycle , the CPU can execute more part instructions  per second. And therefore, the number of clock cycles per second is  known as processor speed . The  processor speed  is expressed  in  Megahertz ( MHz )  OR  Gigahertz  (  GHz  ) .

Central Processing Unit Speed

The  bit  size  of the  CPU registers ( Register width 32 bits OR 64 Bits ) dictates  the  maximum permissible  size  of the  RAM for a system .

For example,  a  32 bit  CPU  and  32 bit OS  the  maximum  RAM  supported is  4 GB  AND For  a  64 bit  CPU  and  64 bit  OS  can technically support  any  size   of  the main memory RAM .

CPU Clock Speed And Instruction Cycle

Clock Speed And Instruction Cycle

CPU Bench Marking Tools

A CPU bench-marking tools are used  to benchmark the CPU performance on various predefined parameters .

A CPU bench-marking tool evaluates the CPU performance based on the outcome of  a series of tests designed to measure the performance of a computer Central Processing Unit ( CPU ).

A CPU bench-marking tools make use of set of standards, or baseline measurements are used to compare the performance of different systems, using the same methods and under the same working conditions.

A standard CPU benchmark test will compare the test system performance on various parameters against the standards for the similar type of CPU used.

The important CPU performance parameters typically measured by a CPU bench-marking tool  includes the CPU Clock speed, the number of instructions executed by the CPU, the registry calls per instruction cycle and the few more factors which indicates the overall architecture efficiency of the CPU and system.

CPU Benchmark Tool

The benchmark standards differ depending upon the  generations of CPU and the most commonly used CPU brand  like Intel and AMD .

The CPU benchmark Tool ( software )  also provides information about the other important devices which affect the overall system performance such as main memory RAM , Operating System , Motherboard , Graphics Card and Chipset.

Why Computer Use Binary ?

Why Computer Understands 0 And 1 ?

All of us know that computer understands the language of only two numbers that is Binary 0 and 1 .  The binary number system  is a base 2 number system  that uses only two numbers 0 and 1 to represent any number.

You may be  wondering , why computer use binary number system instead of using human friendly decimal number system which we are all familiar and use it in our daily life. 

It is a legitimate question to ask why computer understands and execute  programs only in binary machine code. It is also the most important and commonly asked questions in the technical interview.

Let us now discuss the reasons why computer use only binary number system. And the answer to this question lies in the computer system architecture.


Why Computer Use Binary Number System ?

Why Computer Use Binary ?

Central Processing Unit - FAQ

What Is CPU ?

A processor ( CPU ) is an integrated circuit ( IC ). The processor consist of millions of IC chips and each IC chip consist of millions of tiny component called transistor. The Transistor is madeup of silicon which is a semiconductor material .

The processor ( CPU ) controls all the activities of the computer system. And therefore it is referred as brain of the computer system. There are two main computer processor manufacturers  Intel and Advanced Micro Devices ( AMD ). These two companies produce most of the processors used in desktop,  laptops  and  notebooks.

A  Central Processing Unit ( CPU )  performs millions  tasks per second  to execute a  computer program by performing the basic arithmetic, logical, control and input  /  output ( I / O ) operations  as  specified  by the  program  instructions. 

A   CPU  is  placed  on  the  motherboard  in  a  processor  socket  with  locking  liver mechanism   in  order  to  fix  the  processor  chip  properly  into the  processor  socket . The processor socket contains a IC socket in which the processor  chip is firmly mounted . A heatsink  is mounted on the top of the processor chip which  protects  the processor  from  excessive  heat generated.

What are Functions Of the CPU ?

The CPU performs some of the most important functions in a computer System and these functions include :

  • To Perform Arithmetic Calculation Operations.
  • To Perform Logical Operations.
  • To Control Functions Of Other Hardware Components.
  • To Fetch the Data And Program Instructions From Main Memory.
  • To Decode the Program Instructions.
  • To Operate On Data As per Program Instructions.
  • To Store Data After Processing.
  • To Continuously Execute Instruction Cycle / Machine Cycle.


There are two main types of CPU  based on the Instruction Set Architecture :

  1. CISC  – Complex Instruction Set Computing .
  2. RISC. –  Reduced Instruction Set  Computing .
  •    Most desktop or laptop computers use CISC ( Complex Instruction Set Computing ) architecture made by Intel or AMD.
  •    Whereas Smartphones and tablets use RISC ( Reduced Instruction Set  Computing  )  by  ARM architecture.
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