---
title: "Compare RISC and CISC architecture"
subject: "Microprocessor"
chapter: 6
key: "semester_4/microprocessor:risc-vs-cisc"
source: https://www.bctengineer.com/q/semester_4/microprocessor/risc-vs-cisc
site: BCT Engineering
---

# Compare RISC and CISC architecture

Microprocessor · Chapter 6: Advanced Topics

- Asked in: 2074 Bhadra, 6 marks; 2072 Asoj, 6 marks; 2070 Magh, 8 marks; 2068 Magh, 8 marks (asked 4 times)
- Video: [RISC vs CISC | Computer Architecture](https://www.youtube.com/watch?v=bTCuFmY0sUg) — Bina Bhatt
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_4/microprocessor/risc-vs-cisc
- Whole chapter: https://www.bctengineer.com/md/semester_4/microprocessor/chapter-6

## Question

Compare and contrast RISC and CISC architecture.

## Short answer

RISC uses simple fixed-length instructions with load/store architecture and a large register file, while CISC uses complex variable-length instructions with direct memory access. RISC has hardwired control and easy pipelining; CISC has microprogrammed control and smaller code size.

## Answer

**RISC** (Reduced Instruction Set Computer) uses a small set of simple, fixed-length instructions that mostly execute in one clock cycle. **CISC** (Complex Instruction Set Computer) uses a large set of complex, variable-length instructions, where one instruction can do many low-level operations.

| Basis | RISC | CISC |
|---|---|---|
| Instruction set | Small, simple (about 50–150) | Large, complex (200+) |
| Instruction length | Fixed (e.g. 32 bits) | Variable |
| Execution time | Mostly 1 clock cycle | Several clock cycles |
| Addressing modes | Few, simple | Many |
| Memory access | Only LOAD and STORE access memory (load/store architecture) | Many instructions can access memory directly |
| Registers | Large register file (32 or more) | Few registers |
| Control unit | Hardwired (fast, simple) | Microprogrammed |
| Pipelining | Easy and efficient | Difficult |
| Code size | Larger programs (more instructions) | Smaller programs |
| Compiler | Complex compiler work; simple hardware | Simple compiler; complex hardware |
| Power / chip area | Low power, smaller control section | Higher power |
| Examples | ARM, MIPS, SPARC, PowerPC, RISC-V | Intel x86 (8086), Motorola 68000, VAX |

**Example:** to add two memory numbers, CISC uses one instruction such as ADD [A], [B] (in a memory-to-memory machine); RISC uses LOAD R1,A; LOAD R2,B; ADD R3,R1,R2; STORE R3,C.

**Contrast in short:** RISC moves complexity to the software (compiler) so the hardware is simple and fast; CISC puts complexity in the hardware to reduce program size and compiler work. Modern x86 processors translate CISC instructions into RISC-like micro-operations internally.

## Check yourself

The answer's key points as multiple-choice questions, with the correct option and why.

1. How do RISC and CISC differ in memory access?
   A. RISC allows only LOAD and STORE to access memory; many CISC instructions can access memory directly
   B. RISC allows all instructions to access memory
   C. CISC allows only LOAD and STORE
   D. Neither accesses memory directly
   Answer: A. RISC is a load/store architecture. (Key point: Memory access)

2. Which pair correctly describes RISC instructions?
   A. Variable length and many cycles
   B. Fixed length and mostly one clock cycle
   C. Fixed length and many cycles
   D. Variable length and always one cycle
   Answer: B. RISC uses fixed-length, simple instructions that mostly complete in one cycle. (Key point: Instruction format and timing)

3. Where does each approach place the complexity?
   A. RISC in the hardware, CISC in the compiler
   B. Both in the hardware
   C. RISC in the compiler (software), CISC in the hardware
   D. Both in the compiler
   Answer: C. RISC moves complexity to software so hardware is simple and fast; CISC reduces program size using complex hardware. (Key point: Trade-off)

4. Which is true?
   A. RISC uses a hardwired control unit and gives larger programs; CISC is microprogrammed with smaller programs
   B. RISC is microprogrammed with smaller programs
   C. CISC is hardwired with larger programs
   D. RISC has small register file and microcode
   Answer: A. RISC has hardwired control and needs more instructions per task; CISC is microprogrammed with compact code. (Key point: Control unit and code size)

## Related in Microprocessor

- [Hardwired vs microprogrammed control unit](https://www.bctengineer.com/question.md?key=semester_4%2Fmicroprocessor%3Ahardwired-microprogrammed-cu) — Microprocessor, chapter 1, asked 3×

## Related in other subjects

- [RISC vs CISC](https://www.bctengineer.com/question.md?key=semester_5%2Fcomputer_organization_and_architecture%3Arisc-cisc) — Computer Organization and Architecture, chapter 2, asked 5×
- [Compare and contrast pollution in a city](https://www.bctengineer.com/question.md?key=semester_5%2Fcommunication_english%3Acompare-contrast-pollution-city-nepal) — Communication English, chapter 1
- [RISC and efficient instruction pipeline](https://www.bctengineer.com/question.md?key=semester_5%2Fcomputer_organization_and_architecture%3Arisc-pipeline) — Computer Organization and Architecture, chapter 4