What is the CPU?

Table of Contents

The CPU performs almost all the calculations that the computer needs. The CPU also controls the running of the operating system (Windows for example) and the application programs, such as spreadsheets, databases and word processing. The CPU is the most important item in a computer since it controls the overall speed and performance of your computer. The speed of a CPU is related to the frequency of its clock and is measured in Hz. However these speeds are so high that GHz are used to indicate speeds of CPU’s. (1 GHz = 1 GigaHertz = 109 Hertz). Typical speeds are now in the range of 1 to 3 GHz. The higher the speed of the CPU the faster your computer will run however the overall performance of your computer depends also on other hardware such as the RAM of your computer.

Below is shown the diagram of the CPU where the main parts are:

Diagram of a CPU.

Fig. 1 - What makes a CPU?

Arithmetic and Logic Unit (ALU)

The Arithmetic Logic Unit (ALU) is a component of the Central Processing Unit (CPU) in a computer that performs arithmetic and logical operations on binary data.
The ALU is an essential component of the CPU that performs arithmetic and logical operations on binary data. It is responsible for carrying out the complex computations that enable a computer to function.
The arithmetic operations include addition, subtraction, multiplication, and division of binary numbers. The logical operations include AND, OR, NOT, and XOR operations that are used for comparing, shifting, and manipulating binary data.
The ALU is responsible for carrying out these operations by using different types of logic gates and circuits. It performs these operations based on the instructions given by the control unit of the CPU.


Registers are small, fast memory locations in the Central Processing Unit (CPU) of a computer that are used for the temporary storage of data and instructions that the CPU needs to access frequently.
Registers are an essential part of the CPU's architecture and are used to perform arithmetic and logical operations, store addresses, hold status flags, and control the flow of instructions in the CPU. Registers are built directly into the CPU, and their fast access time allows the CPU to perform calculations and process data quickly.
There are several types of registers in a CPU, including the program counter, instruction register, memory address register, memory data register, and general-purpose registers. Each of these registers serves a specific purpose and is used by the CPU to perform various tasks during program execution.

Control Unit

The Control Unit (CU) is a component of the Central Processing Unit (CPU) in a computer that manages the flow of data and instructions within the CPU. The CU is responsible for coordinating all the operations of the CPU and ensuring that each instruction is executed correctly.
The Control Unit receives instructions from memory and decodes them into a series of commands that the CPU can understand. It then sends these commands to the appropriate components within the CPU, such as the Arithmetic Logic Unit (ALU) or the Registers, to perform the required operations.
The CU also controls the timing of the CPU's operations, ensuring that each instruction is executed in the correct sequence. It does this by sending out control signals that synchronize the operations of the CPU's various components.
In addition to managing the flow of data and instructions, the Control Unit also handles error detection and correction. If an error is detected, the CU will take the appropriate action to correct the error or signal the computer to halt its operations.
Overall, the Control Unit is a critical component of the CPU that plays a vital role in ensuring that the computer executes instructions correctly and efficiently.

References and Links

1 - Computer Organization and Design MIPS Edition - The Hardware/Softwa Interface - 6th Edition - November 2020 - By David Patterson, John Hennessy
eBook ISBN: 9780128226742 - Paperback ISBN: 9780128201091
2 - Computer Architecture - A Quantitative Approach - 6th Edition - November 2017 - By John Hennessy, David Patterson
eBook ISBN: 9780128119068 - Paperback ISBN: 9780128119051
3 - Computer Systems: A Programmer's Perspective (3rd Edition) Hardcover – March 2015 - By Randal E. Bryant and David R. O'Hallaron