Central Processing Unit (CPU)

Is the electronic circuitry of a computer responsible for interpreting the instructions of computer programs and executing basic operations according to those instructions. The basic operations include arithmetical, logical, controlling, and input/output(I/O). The term Central Processing Unit (CPU) has been widely used in the computer industry since the early 1960s.

The CPU is composed essentially of four functional units:

• Control Unit: is responsible for controlling the flow of instructions and data within the CPU. 
• Arithmetic Logic Unit (ALU): performs all the arithmetic and logical operations calculations of the CPU.
• Registers: are internal memory cells that can be accessed very fast. These components are used to store variables (data, addresses) or the intermediate results of the arithmetic /logic operation.
• Cache: is a smaller and faster memory that minimize access to the main memory and consequently improve CPU performance.

These units are synchronized by the clock rate and connected by three types of buses:

• Data bus: responsible for conveying data.
• Address Bus: conveys the memory addresses to read or write.
• Control bus: allows the management of other components and I/O devices.

The CPU architecture is also characterized by the set of instructions that it can execute. Generally, there are two types of instruction set architectures:

• CISC (complex instruction set computer): an extensive set of complex instructions that can perform multiple low-level operations such as arithmetic operations, memory access or address calculations in several clock cycles.
• RISC (Reduced instruction set computer): a reduced set of instructions that performs a single low-level operation in one clock cycle.