CISC vs RISC

risc : definition

set made up of a small number of simple, fixed-length instructions

risc: how many lines of machine code does 1 instruction take

1-2

risc: memory

programs are longer and take up more memory

• simple commands so basic tasks require several instructions

risc: speed

simpler instructions = faster to execute = increasing performance of processor

risc: power

require less circuitry = cheaper to design, produce and run + give off less heat and less power consumption

risc: examples

mobile phones, small specialist devices + super computers

risc: why suited for mobile phones, tablet computers , small specialist devices?

lower power requirements of RISC makes them far more suitable for battery-powered devices

risc: why suited for supercomputers?

risc architecture is inherently designed to facilitate parallelism and pipelining

supercomputers have a demand for high-speed parallel processing

risc: size

small - fewer transistors needed to handle smaller cpu instruction set

risc: ram

lots of ram required to store code, which can cause system bottlenecks

risc: compiler

compiler has to do more work to translate high level code into machine code

risc: hardware vs software

software over hardware: high-level compilers take on most of the burden of translating many software steps from the programmer

cisc: definition (complex)

designed to execute complex instructions in as few lines of assembly language as possible

cisc: how do they execute complex instructions in as few lines of assembly language as possible?

carry out a number of low-level operations as part of a single instruction

cisc: memory

more specialised instructions = take up less space in the main memory = easier to translate to machine code

cisc: speed

take several clock cycles to complete = longer to process

cisc: power

leads to large complex cpu w/ many transistors = uses more power + require heat sink/ cooling fan

cisc: examples

• earlier were the standard + traditionally used in specialist computers

• now used in micro controllers + embedded systems

cisc: ram

makes efficient use of ram

cisc: why does it make efficient use of ram

code shorter so less ram needed

cisc: compiler

compiler has less work to translate high level code into machine code

cisc: hardware vs software

hardware over software: the ISA (instruction set architecture) does as much as possible using dedicated processor hardware circuitry