Cs 147 Spring 2010 Meg Genoar

History Started to emerge in mid-1970s 1988 – RISC took over workstation market

CISC Complex Instruction Set Computer Many instructions in its ISA (Instruction Set Architecture) Each instruction: several low-level operations (e.g. load from memory, arithmetic operation, memory store) in a single instruction

Why CISC? Old programming: machine code or assembly language  put complexity into hardware (hardware design is easier than compiler design) Small memories: high program density was advantageous Make one instruction do as much work as possible

Benefits of CISC Smaller program sizes Fewer main memory accesses Lower memory and disc storage cost Faster execution Better programming productivity

Problems High number of clock cycles Less expensive memory  main memory calling is ok Limits on benefits

RISC Reduced Instruction Set Computer Same length instructions Simple instructions Longer Programs

Why RISC? 1980s: CISC was reaching theoretical limits Focus on parallel processing More chips rather than faster chips  parallel computing  divide problems among them Efficient utilization of resources Pipelining  Fast execution

RISC Examples Apple iPod Apple iPhone and iPod Touch Apple iPad Palm and PocketPC PDAs and smartphones Blackberry xbox 360 Nintendo Game Boy Advance Nintendo DS

CISC vs RISC CISCRISC Complex instructions  multiple clock cycles Simple instructions  single clock cycle Instructions executed one at a timePipelining Many instructions reference memoryLoad and Store only Not many general registersMany general registers