1. 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

2. 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.

3. 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

4. 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 ...

5. 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.

6. RISC, CISC architectures tradeoff