The Goal of this class Goal – Learn what are CISC and RISC. CISC/RISC tradeoff. Learning outcome by the end of this class the students should know the main differences and distinguish RISC solutions from the CISC solutions

CISC and RISC approaches As the Memory was expensive – the programs should have been short: Early trend was to add more and more instructions to new CPUs to do elaborate operations In order to have shorter programs to fit into the small memory VAX architecture had an instruction to multiply polynomials. intel x86 had string or array operation instructions. Memory becomes cheaper – the programs could be longer: RISC philosophy – Reduced Instruction Set Computing. Keep the instruction set small and simple, makes it easier to build fast hardware. Let software do complicated operations by composing simpler ones.

Complex Instruction Set Computer Complex and powerful instructions memc = mema + memb Small and expensive Memory z = (a + b)(c + d) arr2[1..n] = arr1[1..n] Short programs with powerful instructions Many different types of instructions bool1 = str1 cmp str2 short long instr longer instr instr . . . Processor (very complex) memc = mema + memb z = (a + b)(c + d) bool1 = str1 cmp str2

Reduced Instruction Set Computer Large and cheap Memory Complex and powerful instructions Many and Long programs with simple instructions memc = mema + memb z = (a + b)(c + d) a = mema arr2[1..n] = arr1[1..n] bool1 = str1 cmp str2 b = memb Many different types of instructions short x = a + b c = a + b long instr y = c + d memc = c longer instr z = x * y instr . . . Processor (very simple but fast with possibility to make parallelism) Simple, uniform size instructions c = a + b a = mema c = a + b z = x * y z = x * y memc = c Few types of instructions inst ...

MIPS Architecture MIPS – semiconductor company that built one of the first commercial RISC architectures. We will study the MIPS architecture in detail in this course. Why MIPS instead of Intel 80x86? MIPS is simple.

RISC, CISC architectures tradeoff