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3 Basic Parts of CPU Explained for Kids Advantage

Basic Parts of CPU

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Nowadays computers are used almost everywhere. Computers are used for various purposes, however, the basic function remains the same – processing the data and giving out the information. The part that is responsible to convert data into information is called the CPU (Central Processing Unit). That’s the reason it’s also called the “Brain of Computer”. Let’s explore the 3 basic parts of CPU.

What is CPU?

A central processing unit (CPU), is also called a central processor, main processor, or just processor. It is an electronic device consisting of circuits that execute instruction comprising a computer program.

The CPU is capable of performing basic arithmetic, logic, controlling, and input/output (I/O) operations specified by the instructions of a program.

The form, design, and implementation of CPUs have changed over the years, but their fundamental operation remains almost unchanged.

Basic Parts of CPU
CPU Chip

Where CPU is Located in a Computer?

CPU is located on a motherboard of a computer. The position of the CPU on the motherboard is chosen depending on various factors. Among this CPU cooling and internal device, temperatures are taken into consideration when deciding the placement of a CPU on a motherboard. 

The topmost CPU manufacturing companies are Intel and Advanced Micro Devices (AMD), although there are many more where CPU is manufactured.

Components of a CPU

The principal components of a CPU are

  • Arithmetic Logic Unit (ALU)
  • Control Unit (CU)
  • Memory (Registers)

Arithmetic Logic Unit

The arithmetic logic unit is that part of the CPU that handles all the calculations the CPU may need. Most of these operations are logical in nature. Depending on how the ALU is designed, it can make the CPU more powerful, but it also consumes more energy and creates more heat. Therefore, there must be a balance between how powerful and complex the ALU is and how expensive the whole unit becomes. This is why faster CPUs are more expensive, consume more power, and dissipate more heat.

The main functions of the ALU are to do arithmetic and logic operations, including bit-shifting operations. These are essential processes that need to be done on almost any data that is being processed by the CPU.

ALUs routinely perform the following operations:

  • Logical Operations: These include AND, OR, NOT, XOR, NOR, NAND, etc.
  • Bit-Shifting Operations: This refers to shifting the positions of the bits by a certain number of places to the right or left, which is considered a multiplication operation.
  • Arithmetic Operations: This refers to bit addition and subtraction. Addition can be used to substitute for multiplication and subtraction for the division. (Although multiplication and division are sometimes used, these operations are more expensive to make.)

Control Unit

The main function of a control unit is to control the operations of a CPU. It also helps in the coordination of operations among other parts of the CPU.

Functions of the control unit are as follows:

  • Controls sequential instruction execution
  • Interprets instructions
  • Guides data flow through different computer areas
  • Regulates and controls processor timing
  • Sends and receives control signals from other computer devices
  • Handles multiple tasks, such as fetching, decoding, execution handling, and storing results

Control units are designed in two ways:

Hardwired control: Design is based on a fixed architecture. The CU is made up of flip-flops, logic gates, digital circuits, and encoder and decoder circuits that are wired in a specific and fixed way. When instruction set changes are required, wiring and circuit changes must be made. This is preferred in a reduced instruction set computing (RISC) architecture, which only has a small number of instructions.

Microprogram control: Microprograms are stored in a special control memory and are based on flowcharts. They are replaceable and ideal because of their simplicity.


The memory present inside the CPU is called Register. The registers are very fast computer memory which is used to execute operations efficiently. For this purpose, there are several different classes of registers which all work in coordination with the computer memory to run operations efficiently. The sole purpose of having a register is the fast retrieval of data for processing by CPU.

These registers are classified as:


An accumulator acts as a temporary storage location that holds an intermediate value in mathematical and logical calculations. Intermediate results of an operation are progressively written to the accumulator, overwriting the previous one.

For example, in the operation “2 + 4 + 1”, the accumulator would hold the value 2, then 6 (2 + 4), then the value 7 (6 + 1).

Memory Address Register (MAR)

It either stores the memory address from where data will be fetched to the CPU or the address to which data will be sent and stored.

It means this register is used to access data and instructions from memory during the execution phase of instruction. MAR holds the memory location of data that needs to be accessed.

Memory Data Register (MDR)

Also known as Memory Buffer Register (MBR) stores the data being transferred to and from the immediate access storage. It contains a copy of designated memory locations specified by the Memory Address Register. 

It acts as a buffer allowing the processor and memory units to act independently without affected by minor differences in operation. A data item will be copied to the MDR ready for use at the next clock cycle when it can be either used by the processor for reading or writing or stored in the main memory after being written.

Program Counter (PC)

A Program Counter contains the address of the instruction being executed at the current time. As each instruction gets fetched, the PC increases its stored value by 1. After each instruction is fetched, the PC points to the next instruction in the sequence. When the computer restarts or is reset, the PC normally reverts to 0.

Instruction Register (IR)

Also known as Current Instruction Register (CIR) holds the instruction currently being executed or decoded. In simple processors, each instruction to be executed is loaded into the IR, which holds it while it is decoded, prepared, and ultimately executed, which can take several steps.

Some of the complicated processors use a pipeline of instruction registers where each stage of the pipeline does part of the decoding, preparation, or execution and then passes it to the next stage.

Condition Code Register (CCR)

Also known as Status Register (SR), Flag Register (FR) is a collection of status flag bits for a processor. CCR contains information about the state of the processor. Individual bits are implicitly or explicitly read and/or written by the machine code instructions executing on the processor. The CCR lets an instruction take action contingent on the outcome of a previous instruction.

Typically flags in the CCR are modified as effects of arithmetic and bit manipulation operations.

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