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RISC / CISC Architecture by Derek Ng
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Overview CISC Architecture RISC Architecture Pipelining RISC vs CISC
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What is CISC Complex Instruction Set Computer “High level” Instruction Set Executes several “low level operations” Ex: load, arithmetic operation, memory store
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Features of CISC Instructions can operate directly on memory Small number of general purpose registers Instructions take multiple clocks to execute Few lines of code per operation
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What is RISC? Reduced Instruction Set Computer RISC is a CPU design that recognizes only a limited number of instructions Simple instructions Instructions are executed quickly
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Features of RISC “Reduced” instruction set Executes a series of simple instruction instead of a complex instruction Instructions are executed within one clock cycle Incorporates a large number of general registers for arithmetic operations to avoid storing variables on a stack in memory Only the load and store instructions operate directly onto memory Pipelining = speed
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Quick Performance
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Pipelining “Assembly Line” Technique to process multiple instructions at the same time Allows instructions to be executed efficiently
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Stages of Pipelining Fetch instructions from memory Decode the instruction Execute the instruction or calculate an address Access an operand in data memory Write the result into a register
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Pipelining Example
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CISC vs RISC CISCRISC Complex instructions require multiple cycles Reduced instructions take 1 cycle Many instructions can reference memory Only Load and Store instructions can reference memory Instructions are executed one at a time Uses pipelining to execute instructions Few general registersMany general registers
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References http://cse.stanford.edu/class/sophomore- college/projects-00/risc/ http://cse.stanford.edu/class/sophomore- college/projects-00/risc/ http://en.wikipedia.org/wiki/Complex_instruction_set_co mputer http://en.wikipedia.org/wiki/Complex_instruction_set_co mputer http://en.wikipedia.org/wiki/RISC http://arstechnica.com/articles/paedia/cpu/pipelining- 1.ars/4 http://arstechnica.com/articles/paedia/cpu/pipelining- 1.ars/4
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