Processor Types

This lesson covers the different types of processors you need to know for OCR H446: CISC vs RISC, multi-core processors, parallel processing, co-processors and GPUs. You must be able to compare these types and explain when each is suitable.

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CISC — Complex Instruction Set Computer

A CISC processor has a large, varied instruction set where individual instructions can perform complex multi-step operations.

Characteristics of CISC

Feature	Detail
Instruction set	Large — hundreds of different instructions
Instruction length	Variable — instructions can be different numbers of bytes
Instruction complexity	Single instructions can perform complex tasks (e.g. multiply and store in one instruction)
Clock cycles per instruction	Variable — complex instructions may take many clock cycles
Addressing modes	Many different addressing modes available
Registers	Fewer general-purpose registers
Hardware	Complex — uses microcode (micro-programs) to implement complex instructions
Compiler complexity	Simpler — the compiler has many powerful instructions to choose from

Examples