1.1.1 Architecture of the CPU
The purpose of the CPU
Figure 1 Input - process - output
All computer systems can be broken down into the figure 1.
A computer system will take in an input, from a mouse or keyboard etc, and process the information it receieves. The system will then give a form out output, be that a cursor moving, or a page chanigng on a website. Sometimes information is stored for later in the systems storage.
The Process and Storage parts of this diagram are completed by the Central Processing Unit (CPU).
The CPU is made up of transistors, which are esentially switches that can either be on or off. Arranging these transistors can create logic gates that can process information and carry out instructions. As you can imagine many transistors switching on and off again can generate lots of heat, because of this CPU's are potected by heat sinks designed to remove that heat and keep the CPU functional.
The fetch-execute cycle
The Fetch-Execute cycle is a process that the CPU continually carried out.
It will be explained briefly here and revisited at the bottom of this page after we have discussed Von Neumann architecture. The purpose of the Fetch-Execute cycle is to:
Fetch the instructions
Decode the instcurctions
Execute the instructions
This process is then repeated constantly while the computer system operates.
Figure 2 Fetch - Execute cycle
Common CPU components and their function
ALU (Arithmetic Logice Unit)
CU (Control Unit)
Cache
Registers
ALU (Arithmetic Logic Unit)
The ALU is the part of the CPU that is in charge of many calculations within the CPU. Those calculations include:
Basic arithmetic operations (add, subtract, multiply, divide)
Logical operations (AND, OR and NOT) - More information on Boolean Logic
Number comparisons (less than, greater than, equal to)
Binary shift operations - More information on Binary Shifts
The diagram on the left is commonly shown with regards to the ALU. However is not needed to be remembered for the GCSE course.