---
title: "RISC and efficient instruction pipeline"
subject: "Computer Organization and Architecture"
chapter: 4
key: "semester_5/computer_organization_and_architecture:risc-pipeline"
source: https://www.bctengineer.com/q/semester_5/computer_organization_and_architecture/risc-pipeline
site: BCT Engineering
---

# RISC and efficient instruction pipeline

Computer Organization and Architecture · Chapter 4: Pipeline & Vector Processing

- Asked in: 2073 Shrawan, 3 marks
- Video: [RISC Pipeline | Delayed Load & Delayed Branch with Example | Computer Organization](https://www.youtube.com/watch?v=B_qs8aWwCVY) — T V Nagaraju Technical
- 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-pipeline
- Whole chapter: https://www.bctengineer.com/md/semester_5/computer_organization_and_architecture/chapter-4

## Question

"RISC has the ability to use efficient instruction pipeline". Justify the statement.

## Short answer

RISC has fixed-length instructions, load/store architecture, uniform one-cycle execution, many registers, few addressing modes, delayed branches, and hardwired control, making pipeline stages balanced and efficient with CPI near 1.

## Answer

RISC makes the instruction pipeline efficient for these reasons:
- **Fixed length, simple instructions** are decoded quickly and in a regular way, so each takes about the same time per stage.
- **Load/store architecture:** only LOAD and STORE access memory, so most instructions do not need operand memory access, and few structural hazards occur.
- **Uniform one-cycle execution** gives balanced stage times, so the pipeline moves smoothly with CPI close to 1.
- **Many registers** keep operands inside the CPU, reducing memory delays.
- **Few addressing modes** make address calculation simple.
- **Delayed branch** lets the compiler fill the slot after a branch, hiding the branch penalty.
- **Hardwired control** is fast and has no microcode delays.

## Check yourself

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

1. Why do fixed-length, simple RISC instructions help the pipeline?
   A. They need microcode
   B. They decode quickly and regularly, taking similar time per stage
   C. They require many addressing modes
   D. They eliminate the clock
   Answer: B. Regular decoding keeps stage times balanced so the pipeline flows smoothly. (Key point: Fixed-length simple instructions)

2. How does the load/store architecture reduce pipeline problems?
   A. Every instruction accesses memory for operands
   B. Only LOAD and STORE access memory, so few structural hazards occur
   C. It removes the need for registers
   D. It makes branches impossible
   Answer: B. Most instructions use registers, so memory conflicts between stages are rare. (Key point: Load/store architecture)

3. What is the purpose of the delayed branch in RISC?
   A. The compiler fills the slot after a branch to hide the branch penalty
   B. It delays all instructions by one clock
   C. It forces the pipeline to be emptied
   D. It removes the need for CPI
   Answer: A. A useful instruction placed in the slot after the branch keeps the pipeline busy. (Key point: Delayed branch)

4. Uniform one-cycle execution leads RISC to a CPI close to:
   A. 0.1
   B. 1
   C. 5
   D. 10
   Answer: B. Balanced one-cycle stages let almost one instruction complete per clock. (Key point: CPI)

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