Whilst it may appear that the CPU is just made up of tiny circuit boards, it actually has four main areas:
- Arithmetic Logic Unit (ALU)
- Control Unit (CU)
- The Registers
- Immediate Access Store
The CPU itself interacts with main memory. In the diagram below, you will see that the main memory (Cache & RAM) are smaller in capacity, but physically closer to the CPU than the secondary storage. This is one aspect that makes them faster.
Arithmetic Logic Unit
The ALU is responsible for the procesing of arithmetic (maths) and logical comparrisons within the CPU. When an instruction requires a logic gate to be used, this is the component that will produce the outcome.
The control unit acts as the manager of the CPU. It sends signals to tell the other components how to respond to the instructions that are recieved. The control unit is able to do this as it has it’s own bus for the ignals called the Control Bus.
Registers are small pieces of memory inside the CPU that hold specifi data. There are five main registers that allow the Fetch Decode Execute cycle to run alongside a number of general purpose registers.
You can read more about the CPU registers here.
Immediate Access Store
The IAS is another name for Main Memory, or the umbrella term for the Cache & RAM together. This is where the instructions and currently running program and data are stored in order to run the computer system. The IAS is much faster than secondary storage allowing the CPU to keep up with the demands of the programs.