The Central Processing Unit (CPU), or simply the "brain" of a computer system, is tasked with interpreting and executing instructions from computer programs, orchestrating fundamental operations. These operations encompass arithmetic, logic, control, as well as input/output (I/O) tasks. Since the early 1960s, the term CPU has been ubiquitously employed within the computing industry.

The CPU is fundamentally composed of four functional units:

- Control Unit (CU): Orchestrates the flow of instructions and data within the CPU. It oversees and directs the activities of other components to ensure seamless cooperation and efficient operation.

- Arithmetic Logic Unit (ALU): Executes all arithmetic and logical computations. Whether it's basic addition and subtraction or intricate logical comparisons, the ALU handles it all.

- Registers: High-speed internal memory cells that swiftly store variables, addresses, or intermediate results from arithmetic/logic operations.

- Cache: A smaller, faster memory designed to minimize main memory access, thereby boosting CPU performance. Cache enables quicker data processing.

These components are synchronized by clock cycles and interconnected via three types of buses:

- Data Bus: Transports data.

- Address Bus: Carries memory addresses for reading or writing.

- Control Bus: Governs the actions of other components and I/O devices.

CPU architecture is also characterized by its instruction set, broadly classified into two categories:

- Complex Instruction Set Computers (CISC): Features a complex instruction set capable of executing multiple low-level operations in multiple clock cycles, such as arithmetic, memory access, or address calculations.

- Reduced Instruction Set Computers (RISC): Employs a streamlined instruction set where each instruction completes one low-level operation per clock cycle.