Instruction set
The complete set of operations a CPU can execute, defined by opcode and operand formats. Instruction sets vary between CPU architectures. Rich instruction sets (CISC) support many operations. Lean instruction sets (RISC) support basic operations.
Real World
ARM's instruction set is used in virtually every smartphone, including Samsung Galaxy and iPhone, while Intel's x86 instruction set dominates laptops — software compiled for one cannot run natively on the other.
Exam Focus
When comparing CISC and RISC instruction sets, always link each characteristic to a concrete consequence (e.g. fixed-length enables efficient pipelining).
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