Cs 147 Spring 2010Meg Genoar

History

Started to emerge in mid-1970s

1988 – RISC took over workstation market

CISCComplex Instruction Set ComputerMany 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 CISCSmaller program sizesFewer main memory accessesLower memory and disc storage costFaster executionBetter programming productivity

ProblemsHigh number of clock cyclesLess expensive memory main memory

calling is okLimits on benefits

RISCReduced Instruction Set ComputerSame length instructionsSimple instructionsLonger Programs

Why RISC?1980s: CISC was reaching theoretical limitsFocus on parallel processingMore chips rather than faster chips

parallel computing divide problems among them

Efficient utilization of resourcesPipelining Fast execution

RISC ExamplesApple iPodApple iPhone and iPod TouchApple iPadPalm and PocketPC PDAs and

smartphonesBlackberryxbox 360Nintendo Game Boy AdvanceNintendo DS

CISC vs RISCCISC RISC

Complex instructions multiple clock cycles

Simple instructions single clock cycle

Instructions executed one at a time

Pipelining

Many instructions reference memory

Load and Store only

Not many general registers Many general registers