RISC vs. CISC. By: Frank Norris. Topics of Discussion:. Technological limitations which lead up to the design philosophies of RISC and CISC RISC and CISC Processor Methodologies Processing Comparisons Today’s Processors – Combining RISC and CISC for better performance.
By: Frank Norris
To multiply two numbers, first load each operand from a location in main memory (locations 1:1 through 6:4) into one of the six registers (A, B, C, D, E, or F). Once loaded, they can be multiplied by the execution unit (or ALU).
1. LOAD [A, 2:3]
2. LOAD [B, 5:2]
3. MULT [A, B]
4. STORE [2:3, A]
Complex instructions operate directly on main memory.
Programmer is no longer required to do a direct call to LOAD and STORE operations as they are now handled by hardware.
Compiler has less work to translate statements in a high level language to assembly language.
Microcode became more difficult to test and debug as systems became more complex requiring numerous patches to fix bugs.
Programmers weren’t using the more complex instructions sets in favor of smaller instructions that accomplished the same result.
The use of memory operands caused structural hazards preventing concurrent execution of instructions. (pipelining)Pros and Cons of CISC: