CISSP Study Guide: All About The Central Processing Unit (CPU)

The central processing unit (CPU) is the computer component that controls system operations. It comprises an arithmetic logic unit (ALU), which runs all arithmetic and logical operations, and a control unit, which processes the decoding of instructions and implementation of the requested instructions. Older computers employed multiple chips to take on the task. There are some functions that require support chips, which are often referred to collectively as a chip set.

The CPU relies on two inputs to run its operations: instructions and data. The data is passed to the CPU where it is shaped and processed in either supervisor or problem state. In a problem state, the CPU works on the data with non privileged instructions. In supervisor state, the CPU executes privileged instructions.

There are two basic forms of CPUs produced for today’s computer systems:

1. Reduced Instruction Set Computing (RISC) uses basic instructions that require a reduced number of clock cycles.
2. Complex Instruction Set Computing (CISC) runs multiple operations for a single instruction.

The CPU can be ranked according to its functionality. However, both the hardware and software must be able to accommodate these features including multitasking (when the CPU handles several tasks at once), multiprogramming (same idea as multitasking but the CPU alternates between processes rather than simultaneous execution), multithreading (which runs multiple concurrent tasks executed within a single process), and multiprocessing (where a system contains more than one CPU).