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An instruction set, or instruction set architecture (ISA), is a list of all the commands (instructions), with all their variations, that a processor can execute.

Instructions include:

Arithmetic such as add and subtract
Logic instructions such as and, or, and not
Data instructions such as move, input, output, load, and store
Control flow instructions such as goto, if ... goto, call, and return.

Instruction set architecture is distinguished from microarchitecture. Microarchitecture is the detailed description of the system that is enough for completely describing the operation of all parts of the computing system, as well as how they are inter-connected and inter-operate to implement the ISA. An instruction set is the part of the computer architecture related to programming. An ISA includes a specification set of opcodes (machine language), which are the native commands implemented in a particular central processing unit design. There are 2 variations of the instruction set, CISC and RISC.

Computers with different microarchitectures can share a common instruction set. For example, the Intel Pentium and the AMD Athlon implement nearly identical versions of the x86 instruction set, but they are very different in internal designs.