Central processing unit

The central processing unit (CPU) is the part of a computer that interprets and carries out the instructions contained in the software. In most CPUs, this task is divided between a control unit that directs program flow and one or more execution units that perform operations on data. Almost always, a collection of registers is included to hold operands and intermediate results. The term CPU is often used vaguely to include other centrally important parts of a computer such as caches and input/output controllers, especially in computers with modern microprocessor chips that include several of these functions in one physical integrated circuit. Manufacturers and retailers of desktop computers often erroneously describe the system unit (computer case and its contents) as the CPU; rather, the CPU, as a functional unit, is that part of the computer which actually executes the instructions (add, subtract, shift, fetch, etc.). A family of CPU designs is often referred to as a CPU architecture.

Notable CPU architectures include:

\n* Intel's x86 architecture\n* Zilog's z80 architecture\n* IBM's System/360 architecture\n* DEC's PDP-11 architecture, and its successor, the VAX architecture\n* Motorola's 68000 architecture\n* Sun Microsystems's SPARC architecture\n* MIPS Computer Systems Inc's MIPS architecture\n* HP's PA-RISC architecture\n* DEC's Alpha architecture\n* The AIM Alliance's PowerPC architecture\n* The Advanced RISC Machines (originally Acorn) ARM and StrongARM/XScale architectures\n* SuperH's SuperH architecture\n* UNIVAC 1100/2200 series architecture (currently supported by Unisys ClearPath IX computers)\n* 1750A, the U.S.'s military standard computer.\n* AP-101, the space shuttle's computer

Emerging new CPU architectures include:

\n* Intel's Itanium architecture\n* AMD's x86-64 architecture\n* IBM's Power 5 architecture

Historically important CPUs have been:

\n* EDSAC- the first practical stored-program computer\n* Apollo Guidance Computer, used in the moon flights The above processor architectures could also be characterized by their CPU design like register size. Today most desktop computers have 32-bit processors; 64-bit processors are being phased in. Smaller devices like mobile phones, PDAss, or portable video game devices may have 16 or 8-bit processors.

See also

• arithmetic and logical unit\n* BIOS\n* clock rate\n* computer bus\n* computer engineering\n* CPU cooling\n* CPU design\n* CPU locking\n* CPU power consumption\n* floating point unit\n* front side bus\n* instruction pipeline\n* microcode\n* motherboard\n* wait state

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