Microprocessor Tutorial Microprocessor


Control Unit
Register Array
System Bus


Map of simplified CPU structure. Click on components for more details. Arithmetic and Logic Unit Register Array Control Unit System Bus Memory
The simplified model of the central processing unit. Click on an area for more details.
As there are a great many variations in architecture between the different kinds of CPU, we shall begin my looking at a simplified model of the structure. The model to be used can be seen on the right of this page, and is a good basis on which to build your knowledge of the workings of a microprocessor. The simplified model consists of five parts, which are:

Arithmetic & Logic Unit (ALU)
The part of the central processing unit that deals with operations such as addition, subtraction, and multiplication of integers and Boolean operations. It receives control signals from the control unit telling it to carry out these operations. For more, click the title above.

Control Unit (CU)
This controls the movement of instructions in and out of the processor, and also controls the operation of the ALU. It consists of a decoder, control logic circuits, and a clock to ensure everything happens at the correct time. It is also responsible for performing the instruction execution cycle. More on the control unit can be discovered by clicking the title above.

Register Array
This is a small amount of internal memory that is used for the quick storage and retreival of data and instructions. All processors include some common registers used for specific functions, namely the program counter, instruction register, accumulator, memory address register and stack pointer. For more, click the title above.

System Bus
This is comprised of the control bus, data bus and address bus. It is used for connections between the processor, memory and peripherals, and transferal of data between the various parts. Click the title above for more.

The memory is not an actual part of the CPU itself, and is instead housed elsewhere on the motherboard. However, it is here that the program being executed is stored, and as such is a crucial part of the overall structure involved in program execution. For further information on the memory, please see the seperate tutorial if available.

For more information on these parts of the CPU, click the corresponding title of the description above. You could also click on the part in question on the diagram to the right. Alternatively, click the right arrow button below to move on to the next page, which looks at the arithmetic and logic unit.

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© Matthew Eastaugh, 2004