Computer Central Processing Unit, CPU- what it is & how it works

The central processing unit or CPU is the heart of any computer or embedded system. It is where the actual processing occurs within the computer system .

Computer Technology Includes:
How a computer works CPU central processing unit Computer RAM

The central processing unit or CPU within any computer is where the actual computation occurs - it can be called the brain within the computer.

As such, the CPU is a particularly key area of any computer system small or large.

Central processing unit definition

It is sometimes useful to be able to define CPU and understand exactly what it is: its functions; boundaries; and its operation. In this way it is possible to understand which part of a computer the CPU is.

The central processing unit, CPU is sometimes referred to simply as the central processor, is defined as the primary component of a computer that processes instructions.

Another CPU definition is that the CPU is that part of a computer that performs logical and arithmetical operations on the data as specified in the instructions.

Computer CPU basics

A modern CPU is typically composed of several interconnected blocks, each with a specific function. While the exact architecture may vary between different CPU models, the core components remain consistent:

Control unit, CU: The Control Unit elements of the central processing unit extracts instructions from memory and decodes and executes them, and it uses the ALU where necessary.
Arithmetic logic unit, ALU: Within the central processing unit, the ALU performs arithmetic and logical operations: addition, subtraction, multiplication, division as well as logica operations: AND, OR, NOT, etc. In other words it processes the data to give results.

In some microprocessors the ALU is subdivided into two sections
- Arithmetic Unit, AU: This element of the central processing unit undertakes the purely arithmetic functions of adding, subtracting, etc.
- Logic Unit, LU: The logic unit within the central processing unit undertakes the logic or Boolean functions: AND; NAND; OR; NOR; IF, etc.
Registers: Registers are high-speed storage locations within the CPU that hold data and instructions temporarily. They are used to store intermediate results, addresses, and other essential information.
Cache Memory: Cache memory is a small, high-speed memory unit that stores frequently accessed data and instructions. It acts as a buffer between the CPU and the main memory, reducing access time and improving overall performance.
Interconnect: The interconnect is the network of wires and buses that connect the various components of the CPU, allowing data and control signals to flow between them.

Operation of the CPU

To gain a better understanding of how the CPU works, it can be helpful to look at the functions it performs in greater details.

Fetching: The control unit fetches the next instruction from memory, using the program counter to keep track of the current instruction address.
Decoding: The control unit decodes the fetched instruction, determining the operation to be performed and the operands involved.
Executing: The control unit sends appropriate signals to the ALU and other components to execute the instruction. The ALU performs the necessary calculations or logical operations.
Storing: The results of the operation are stored in a register or memory location, as specified by the instruction.
Incrementing the Program Counter: The control unit increments the program counter to point to the next instruction to be executed, and the cycle repeats.

Factors that affect CPU performance

In order to better grasp what causes some CPUs and hence computers to work faster than others, it's worth taking a look at some of the main factors that govern this.

Clock Speed: The clock speed determines how quickly the CPU can execute instructions. A higher clock speed generally translates to better performance.
Number of Cores: Modern CPUs often have multiple cores, allowing them to execute multiple instructions simultaneously. This can significantly improve performance for tasks that can be parallelized.
Cache Size and Type: A larger cache can store more frequently accessed data, reducing the need to access main memory. The type of cache (e.g., L1, L2, L3) also affects performance.
Instruction Set Architecture (ISA): The ISA defines the set of instructions that a CPU can execute. A more efficient ISA can lead to better performance.
Microarchitecture: The internal design and organization of the CPU's components can also impact performance.

The Central Processing Unit is the heart and soul of a computer system. Its ability to execute instructions, process data, and control the flow of information is essential for any computation or task. By understanding the main blocks of a CPU and how they work together, we gain a deeper appreciation for the complex machinery that powers our digital world.