Central processing unit

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Central processing unit

A central processing unit (CPU) is the primary electronic circuitry within a computer that executes instructions defined by a program. CPUs perform basic arithmetic, logic, control, and input/output (I/O) operations specified by the instructions. The term has been in use since the early 1960s, when mainframe computers used physically separate processor units.

Modern CPUs are implemented on one or more integrated circuits called microprocessors. They contain at least one processing core, with each core capable of executing instructions independently. The CPU is often regarded as the "brain" of the computer, handling the fetch-decode-execute cycle that drives all software.

History

The earliest CPUs were constructed from vacuum tubes and relays. In 1971, Intel introduced the first commercially available microprocessor, the Intel 4004. During the 1970s and 1980s, CPUs evolved from 8-bit designs (e.g., the Intel 8080, MOS Technology 6502) to 16-bit and 32-bit architectures (e.g., the Intel 386). The 1990s saw the rise of 64-bit processors, superscalar execution, and multi-core designs.

The introduction of RISC (Reduced Instruction Set Computer) architectures, such as the ARM architecture and MIPS, shifted the balance from complex instruction sets to simpler, more efficient designs. By the 2010s, CPUs had adopted simultaneous multithreading (SMT) and advanced branch prediction to improve performance.

Features

Key features of a modern CPU include:

• Clock speed: Measured in gigahertz (GHz), the clock speed indicates how many cycles per second the processor can execute.
• Number of cores: A core is an independent processing unit. Dual-core, quad-core, and many-core processors allow parallel execution of tasks.
• Cache memory: Small, fast memory layers (L1, L2, L3) that store frequently accessed data to reduce latency.
• Instruction set architecture (ISA): The set of machine-level instructions the CPU can execute. Common ISAs include x86-64, ARM, and RISC-V.
• Thermal design power (TDP): The maximum amount of heat the cooling system must dissipate, usually measured in watts.
• Integrated memory controller: Allows direct communication with system RAM, often reducing latency.
• Vector processing extensions: Such as SSE, AVX (x86) or NEON (ARM), enabling efficient operation on multiple data elements in a single instruction.

Modern CPUs also incorporate security features like hardware-enforced memory encryption and virtualization support.