---
title: "RISC vs CISC"
subject: "Computer Organization and Architecture"
chapter: 2
key: "semester_5/computer_organization_and_architecture:risc-cisc"
source: https://www.bctengineer.com/q/semester_5/computer_organization_and_architecture/risc-cisc
site: BCT Engineering
---

# RISC vs CISC

Computer Organization and Architecture · Chapter 2: Central Processing Unit

- Asked in: 2078 Bhadra, 6 marks; 2075 Asoj, 6 marks; 2072 Chaitra, 6 marks; 2071 Shrawan, 4 marks; 2069 Asar, 5 marks (asked 5 times)
- Video: [L-2.13: RISC vs CISC | Computer Organization & Architecture](https://www.youtube.com/watch?v=ZW1gb3h-f9k) — Gate Smashers
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_5/computer_organization_and_architecture/risc-cisc
- Whole chapter: https://www.bctengineer.com/md/semester_5/computer_organization_and_architecture/chapter-2

## Question

Differentiate / compare RISC and CISC architecture.

## Short answer

RISC uses a small set of simple, fixed-length, one-cycle instructions with load/store architecture and hardwired control, enabling easy pipelining but larger code. CISC employs complex, variable-length, multi-cycle instructions with microprogramming, reducing code size but complicating design and pipelining.

## Answer

RISC (Reduced Instruction Set Computer) uses a small set of simple, fixed-length instructions that execute in about one clock cycle. CISC (Complex Instruction Set Computer) uses a large set of complex, variable-length instructions, some of which do multi-step work.

| Basis | RISC | CISC |
|---|---|---|
| Instruction set | Small (about 50–100), simple | Large (200 or more), complex |
| Instruction length | Fixed (e.g. 32 bits) | Variable |
| Execution | Mostly one cycle per instruction | Many cycles, varying |
| Addressing modes | Few (3–5) | Many |
| Memory access | Only LOAD and STORE access memory (load/store architecture) | Many instructions access memory directly |
| Registers | Large register file (32 or more) | Few registers |
| Control unit | Hardwired, fast | Microprogrammed, slower |
| Pipelining | Easy and efficient | Difficult |
| Code size | Larger programs (more instructions) | Smaller programs |
| Compiler | More work for the compiler | Less work, hardware does more |
| Cost / design time | Cheaper, simpler chip | Complex, costly |
| Examples | ARM, MIPS, SPARC, PowerPC | Intel x86, VAX, Motorola 68000 |

## Check yourself

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

1. Which is true for RISC instructions?
   A. Variable length and multi-cycle
   B. Fixed length and mostly one cycle
   C. Microprogrammed
   D. Many addressing modes
   Answer: B. RISC uses simple fixed-length instructions. (Key point: Instruction length)

2. In a RISC machine, which instructions access memory?
   A. All arithmetic instructions
   B. Only jumps
   C. Only I/O
   D. Only LOAD and STORE
   Answer: D. This is load/store architecture. (Key point: Memory access)

3. RISC typically uses which control unit?
   A. Microprogrammed
   B. Hardwired
   C. Neither
   D. Both equally
   Answer: B. Hardwired is faster. (Key point: Control unit)

4. Which statement about code size is right?
   A. RISC programs are smaller
   B. They are equal
   C. CISC programs are larger
   D. RISC programs are larger; CISC programs are smaller
   Answer: D. RISC needs more instructions for the same task. (Key point: Code size)

## Related in Computer Organization and Architecture

- [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
- [Computer architecture vs organization](https://www.bctengineer.com/question.md?key=semester_5%2Fcomputer_organization_and_architecture%3Aarch-vs-org) — Computer Organization and Architecture, chapter 1, asked 5×
- [Programmed vs interrupt-driven vs DMA](https://www.bctengineer.com/question.md?key=semester_5%2Fcomputer_organization_and_architecture%3Aio-techniques-compare) — Computer Organization and Architecture, chapter 7, asked 5×
- [Hardwired vs microprogrammed control](https://www.bctengineer.com/question.md?key=semester_5%2Fcomputer_organization_and_architecture%3Ahardwired-vs-micro) — Computer Organization and Architecture, chapter 3, asked 4×
- [Restoring vs non-restoring division](https://www.bctengineer.com/question.md?key=semester_5%2Fcomputer_organization_and_architecture%3Arestoring-vs-nonrestoring) — Computer Organization and Architecture, chapter 5, asked 5×
- [Tightly vs loosely coupled multiprocessors](https://www.bctengineer.com/question.md?key=semester_5%2Fcomputer_organization_and_architecture%3Atight-loose-coupled) — Computer Organization and Architecture, chapter 8, asked 3×

## Related in other subjects

- [Compare RISC and CISC architecture](https://www.bctengineer.com/question.md?key=semester_4%2Fmicroprocessor%3Arisc-vs-cisc) — Microprocessor, chapter 6, asked 4×