What is CPU in Computer | Parts, Functions

The Central Processing Unit (CPU) or simply processor is considered as the “brain” of any computer. It is the most important component or element of a computer system in terms of computing power.

It is located in the CPU socket onto the computer motherboard. Sometimes, it is also called a microprocessor. In today’s computer, the user can easily identify the processor on the motherboard.

Either a fan or heat sink (usually both) is attached from this component. This device draws away the heat a processor produces because heat is  an enemy of electronic components. Heat may damage them.

Every computer has at least one central processing unit or processor. This component performs most of the calculations and performs 90 percent of all the computer’s functions.

A CPU or processor reads data, processes (calculates) the data according to the program instructions, and gives the results of the calculations. The data in the instructions tells the CPU processor what to do.

Physical Composition of a Modern CPU

Physically, a modern central processing unit (CPU) is an electronic chip that is a small, thin, and square shaped sheet of semiconductor material (usually silicon). It contains a complex array of millions of tiny transistors and buses stamped into it with a die.

A “die” refers to a small surface area (typically measured in square mm2) of the chip on which the integrated circuit components of the CPU are fabricated. It is the core component of a CPU where all the transistors, logic gates, and other electronic components are etched onto a silicon wafer that performs the CPU’s calculations and operations.

The die houses millions, or even billions of transistors, interconnected by intricate wiring patterns. These transistors and interconnections form the complex circuits that is responsible for executing instructions and performing calculations within the CPU.

The size of the CPU die varies depending on the manufacturing process and the complexity of the CPU design. Smaller die sizes are generally more efficient, and higher-performing CPUs because they allow for increased transistor density and shorter interconnect distances. Smaller size of die consumes less power.

Once the CPU die is fabricated, it is typically packaged into a sturdy ceramic and metal casing that protects it. This is because a CPU is a fragile. The underside of this casing contains tiny metal pins or dots at precisely spaced that align with connectors on the motherboard’s CPU socket.

The packaging ensures the die’s protection from external elements and provides the necessary electrical connections for communication with other components of the computer system. Each metal pin or dot is a separate communication line that carries a different set of data.

For example, there is a below figure which shows both sides of a CPU designed for a desktop PC.

Physical composition of CPU processor

These metal pins or dots establish the electrical connection between the CPU and the motherboard when inserted into the socket. They allow the CPU to receive power and communicate with other components on the motherboard.

A heat spreader is a metal plate located on top of the CPU die. Its primary function is to dissipate heat generated by the CPU during operation. The heat spreader helps disperse the heat across its surface that efficiently transferred to a cooling solution such as a heat sink or fan.

A heat sink is a device that dissipates heat away from the CPU to prevent overheating. A case fan attached on the CPU circulates the air for further heat removal so that CPU operates within safe temperature limits.

A thermal interface material (TIM) is a substance applied between the CPU die and the heat spreader, which improves heat transfer by filling microscopic gaps and irregularities. It ensures the efficient thermal conduction from the CPU to the heat spreader and, subsequently, to the cooling system.

CPUs come in different sizes and must match with the corresponding CPU socket mounted on the motherboard. The elements inside a CPU are so small that we need a microscope to see them. A common semiconductor element silicon is used in making CPUs because it does not affect the flow of electricity in any way. A semiconductor material neither conducts nor hinders the electrical flow.

Components or Parts of CPU (Central Processing Unit)

The core central processing unit is the main chip or processor that connects onto the computer motherboard. It is a brain of any computer machine. A CPU involves three primary sections. They are as:

  • Control unit (CU)
  • Arithmetic and logic unit (ALU)
  • Registers

The block diagram below illustrates the primary components of a computer and its peripheral devices.

Components or Parts of CPU

Arithmetic Logic Unit (ALU)

The arithmetic and logic unit is a specialized circuit that performs mathematical calculations and logical operations on the data. It works like a calculator, which performs the calculation as directed by the control unit.

ALU can perform all the basic arithmetic functions, such as addition, subtraction, multiplication, and division. In addition, the ALU handles logical operations like AND, OR, and NOT, which are essential for decision-making and data processing. ALU can also perform complex tasks. A CPU may have more than one ALU to carry put the specific functions.

Control Unit (CU)

A control unit is an electronic circuit that is connected by all the parts of a computer. The function of a control unit is to coordinate all the processor’s activities and manage the flow of information through the processor. It directs the flow of data and instructions between different parts of a computer.

The control unit receives the information from the input devices, fetches the data and instructions from the memory, and then reads each instruction to carry out appropriate action. Remember that the control unit itself does not execute any instruction but instructs to other parts of the system, such as ALU, to do so.

For instance, if an application program lets an instruction to multiply three numbers, the control unit directs the task to the ALU, which does the calculation.

Thus, the control unit acts as a mediator for controlling and processing instructions. The main task of a CPU is to control or monitor and manages the functioning of all parts of the computer. It doesn’t participate in data processing or storage.


Registers are a small specialized internal memory within the CPU itself. They act as a temporary storage area for storing data and instructions during processing. They are also called general-purpose registers.

Registers provide high-speed accessing to data and execute instructions quickly. There are various types of registers within the processor. Each serves a specific purpose in the CPU’s operation. They are as:

  • Current instruction register
  • Accumulator
  • Memory address register
  • Memory data/buffer register
  • Program counter
  • Status register

Current instruction register (CIR): This register stores the current instruction being decoded and executed.

Accumulator (ACC): ALU uses this register to temporarily store data during the calculation.

Memory address register (MAR): This register stores the address of the memory location currently being read from or written to.

Memory data register (MDR): This register stores the data which has just read from the memory or data which is about to be written to the memory.

Program counter (PC): This register stores the address where the next instruction is to be fetched.

Status Register (SR): This register contains bits which can be set or cleared depending on the operations.

System Clock

The system clock generates the timing signals required for the synchronization of various CPU operations. It generates clock pulses at a specific frequency, commonly known as the clock speed.

A clock speed determines the number of instructions a CPU processor can execute per second. A higher clock speed generally results in faster processing, but it also affects power consumption and heat generation.

Cache Memory

Cache memory is a special type of high-speed memory that helps to improve the CPU performance. It serves as a buffer between the CPU and main memory (RAM) that provides the much faster data access than RAM. Cache memory is closely located within the CPU itself.

This memory stores frequently accessed data and instructions, enabling faster retrieval and reducing the CPU’s dependence on slower main memory.

When a CPU reads data from the memory, then it will first check out the cache and then move on to the main memory RAM if the required data is not present there. Larger the size of cache memory, the better the performance of CPU.

In this tutorial, we have discussed the central processing unit (CPU) and its various components or parts. Hope that you will have understood the basic points and enjoyed this tutorial.
Thanks for reading!!!

Please share your love