Central Processing Unit
Overview
The Central Processing Unit (CPU) is the primary component of a computer that performs most of the processing inside the computer. It is often referred to as the "brain" of the computer as it carries out the instructions of a computer program by performing basic arithmetic, logical, control and input/output (I/O) operations specified by the instructions.
Architecture
The architecture of a CPU, also known as the microarchitecture, involves the design and organization of the CPU's components. This includes the data path, the control unit, memory management and I/O interfaces. The architecture of a CPU can be categorized into three types: Single-core, Multi-core and Many-core.
A single-core processor has one core. It can execute one instruction at a time. The multi-core processor has two or more cores, which allows it to execute multiple instructions at once. The many-core processor has a large number of cores (typically more than 8), and is designed for parallel processing.
Instruction Set Architecture
The Instruction Set Architecture (ISA) is the part of the processor that is visible to the programmer or compiler writer. The ISA serves as the boundary between software and hardware. It includes the native data types, instructions, registers, addressing modes, memory architecture, interrupt and exception handling, and external I/O.
There are two types of ISAs: Complex Instruction Set Computing (CISC) and Reduced Instruction Set Computing (RISC). CISC has many specialized instructions, some of which may only be rarely used in practical programs. RISC has a smaller set of more general instructions.
Performance
CPU performance can be measured in several ways, including clock speed, instructions per cycle (IPC), and transistor count. Clock speed refers to the number of cycles that a CPU can perform in a second. IPC refers to the number of instructions that can be executed for each clock cycle. Transistor count refers to the number of transistors on the CPU.
Power Consumption and Heat Dissipation
Power consumption and heat dissipation are significant challenges in modern CPU design. As the number of transistors on a chip increases, so does the power consumption. This, in turn, increases the amount of heat that must be dissipated. Techniques for managing power consumption and heat dissipation include dynamic voltage and frequency scaling, dynamic power gating, and thermal design power.