1. Differences in ISA Instruction length
Fixed versus variable, 2 byte to 57 byte
Number of different instructions (opcodes)
Addressing modes
Number and Type of operands
Stack, Accumulator, Multiple Register, Memory
Size of operands (related to length)

2. Number of Instructions
RISC: Reduced instruction set computer
Fewer instructions
Fixed length
Short opcode
CISC: Complex instruction set computer
More instruction
Variable length
Longer opcode

3. Example: Subtraction C=A-B
RISC:
LOAD R1, A
LOAD R2, B
NOT R2, R2
ADD R2, R2, 1
ADD R2, R2, R1
STORE C,R2
CISC:
SUBMEM C, A, B

4. Which is better? Better in what terms? Speed Cost of production
Cost of development
Flexibility for improvement

5. Better in terms of speed?
RISP:
many instruction
one cycle per instruction
High cycle time
CISP:
few instruction
Multiple cycle per instruction
Low cycle time
No clear answer!

6. Examples for CISC and RISC
Intel Pentium
AMD
IBM 390
RISC
HP PA
Motorola, IBM,Apple: PowerPc
Sun Ultra: SPARC