The central processing unit, more commonly referred to as the processor, is the brain behind the computer. There are three primary components that make up the central processing unit (CPU). These components carry out the instructions that allow the computer to function.
Arithmetic Logic Unit
The Arithmetic Logic Unit (ALU) contains the electrical circuits that are used to carry out instructions. The processor can execute many different types of instructions, such as addition, subtraction, multiplication, division, exponentiation, logarithms, etc… The processor can carry out logical instructions such as, greater than, less than, equal to, and so on.
The registers are tiny storage components located on the processor. The registers are used to store data that is needed frequently, or quickly. Because registers are located on the processor, they are incredibly fast. Registers are volatile storage, meaning, they are unable to maintain data storage without a power source.
An example usage of registers is the addition of two numbers. Each of the numbers to be added are stored in a register on the processor. The ALU will pull these numbers out of the registers, add them together, and then, store the sum into another register. Data is constantly moving in and out of the registers.
The control unit has two primary functions within the processor. Just as its name implies, the control unit oversees moving data around inside of the processor. It can pull data out of the registers, or move new data into them. It is also able to access program instructions and feed commands into the ALU.
The control unit is also in charge of external data movement between the processor, primary and secondary storage devices, and other I/O devices.
Registers offer incredible speed. They are faster than primary storage devices, such as RAM. The primary reason why this type of memory is not standard throughout the computer, is because of its cost. This type of storage is extremely expensive, and not practical for general usage; therefore, slower, cheaper memory, such as RAM, is normally used for primary storage.