---
title: "Tightly vs loosely coupled multiprocessors"
subject: "Computer Organization and Architecture"
chapter: 8
key: "semester_5/computer_organization_and_architecture:tight-loose-coupled"
source: https://www.bctengineer.com/q/semester_5/computer_organization_and_architecture/tight-loose-coupled
site: BCT Engineering
---

# Tightly vs loosely coupled multiprocessors

Computer Organization and Architecture · Chapter 8: Multiprocessors

- Asked in: 2078 Kartik, 4 marks; 2074 Asoj, 4 marks; 2069 Asar, 4 marks (asked 3 times)
- Video: [Classification of multiprocessor systems/Difference tightly and loosely coupled syst- lecture70/coa](https://www.youtube.com/watch?v=9jTBjLi-o4k) — asha khilrani
- 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/tight-loose-coupled
- Whole chapter: https://www.bctengineer.com/md/semester_5/computer_organization_and_architecture/chapter-8

## Question

Differentiate between tightly coupled multiprocessors and loosely coupled multiprocessors.

## Short answer

Tightly coupled multiprocessors share a common memory and communicate through it, providing fast, low-latency interaction but limited scalability. Loosely coupled systems have distributed local memories and communicate via message passing, offering higher scalability with slower, higher-latency communication.

## Answer

| Point | Tightly coupled | Loosely coupled |
|---|---|---|
| Memory | Common shared memory used by all processors | Each processor has its own local memory |
| Communication | Through the shared memory | By message passing over a message-transfer system |
| Interconnection | Bus, crossbar or multistage network | Communication channels, links, networks |
| Interaction | High, strong interaction between processors | Low, minimal interaction |
| Data rate and delay | Fast, low delay | Slower, high delay |
| Memory contention | Yes, a bottleneck | No, local memory |
| Scalability | Limited | Easily scaled to many processors |
| Suitable for | Parallel tasks with shared data | Distributed tasks, clusters |
| Example | SMP server | Cluster of computers |

## Check yourself

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

1. How is memory organised in tightly coupled multiprocessors?
   A. Each processor has only local memory
   B. No memory is used
   C. Only disk is used
   D. A common shared memory is used by all processors
   Answer: D. Tightly coupled systems share a common memory. (Key point: Memory)

2. How do loosely coupled processors communicate?
   A. By sharing registers
   B. By sharing the ALU
   C. Through shared memory
   D. By message passing over a message-transfer system
   Answer: D. Each has local memory and uses messages. (Key point: Communication)

3. Which system has memory contention as a bottleneck?
   A. Both have none
   B. Loosely coupled
   C. Neither
   D. Tightly coupled
   Answer: D. Shared memory causes contention; loosely coupled has local memory. (Key point: Contention)

4. Which scales more easily to many processors?
   A. Neither
   B. Loosely coupled
   C. Both equally limited
   D. Tightly coupled
   Answer: B. Loosely coupled systems like clusters scale easily; tightly coupled is limited. (Key point: Scalability)

## Related in Computer Organization and Architecture

- [Tightly-coupled multiprocessor](https://www.bctengineer.com/question.md?key=semester_5%2Fcomputer_organization_and_architecture%3Atightly-coupled) — Computer Organization and Architecture, chapter 8