Early computers such as the ENIAChad to be physically rewired to perform different tasks, which caused these machines to be called "fixed-program computers". The "central processing unit" term has been in use since as early as

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The fundamental operation of most CPUs, regardless of the physical form they take, is to execute a sequence of stored instructions that is called a program. The instructions to be executed are kept in some kind of computer memory. Nearly all CPUs follow the fetch,

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Hardwired into a CPU's circuitry is a set of basic operations it can perform, called an instruction set. Such operations may involve, for example, adding or subtracting two numbers, comparing

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Cloud computing can involve subdividing CPU operation into virtual central processing units (vCPUs ).
A host is the virtual equivalent of a physical machine, on which a virtual system is operating. When there are several physical machines

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The performance or speed of a processor depends on, among many other factors, the clock rate (generally given in multiples of hertz) and the instructions per clock (IPC), which together are

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• Addressing mode
• AMD Accelerated Processing Unit
• CISC
• Computer bus

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1. ^ Integrated circuits are now used to implement all CPUs, except for a few machines designed to withstand large electromagnetic pulses, say from a nuclear weapon.

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