Central Processing Unit, CPU

- 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 .

The central processing unit or CPU within any computer is where the actual computation occurs. As such, the CPU is a particularly key area of any computer or embedded system.

Typically, embedded systems will only have a single CPU, but it is possible for a computer to have more and this is referred to as multiprocessing.

The CPU contains all the arithmetic units and is able to provide the addition, subtraction and logical functions.

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 or embedded system 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.

CPU basics

Within a central processing unit, whether it is used for an embedded system, a laptop, desktop, or a much larger computer there are typically two main units.

  • Arithmetic logic unit, ALU:   Within the central processing unit, the ALU performs arithmetic and logical operations.
  • 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.

CPU arithmetic logic unit, ALU

The arithmetic logic unit, ALU is one of the main functional blocks within a computer or embedded system central processing unit.

The ALU performs all the processes related to arithmetic and logic operations that need to be done on instruction words.

In some microprocessors the ALU is subdivided into two further sections that are optimised for different functions:

  • 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.

Even if these two entities are not separated out, the CPU will need to handle both functions.

By Ian Poole

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