CISC - Complex Instruction Set Computer

Processors designed with full set of instructions to provide functions in the most efficient way.

CISC has the capacity to perform multi-step operations or addressing modes within one instruction set. It is the CPU design where one instruction works several low-level acts. For instance, memory storage, loading from memory, and an arithmetic operation.

Unlike RISC, CISC instructions can perform complex tasks that take more than one cycle to execute. These can include floating-point mathematical calculations and graphics-handling instructions. CISC can be highly efficient in terms of the number of instructions per program, resulting in lower demand for code storage and RAM compared to RISC. On the other hand, a CISC processor must contain more transistors to handle the complexity of the instructions.

CISC architectures, like the x86, excel in environments where software longevity and legacy support are critical, such as business and enterprise systems. CISC’s broad instruction set enables it to efficiently run older applications without requiring modification, ensuring software continuity.

They allow programmers to optimise performance for specific tasks, such as string manipulation or complex mathematical operations, by closely mapping instructions to hardware.

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