---
title: "DOS; monolithic and microkernel"
subject: "Distributed System"
chapter: 3
key: "semester_7/distributed_system:dos-monolithic-microkernel"
source: https://www.bctengineer.com/q/semester_7/distributed_system/dos-monolithic-microkernel
site: BCT Engineering
---

# DOS; monolithic and microkernel

Distributed System · Chapter 3: Operating System Support

- Asked in: 2075 Asoj, 2+4 marks
- Video: [Difference between monolithic and micro kernel in OS](https://www.youtube.com/watch?v=OAl60mDiZc8) — LS Academy for Technical Education 
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_7/distributed_system/dos-monolithic-microkernel
- Whole chapter: https://www.bctengineer.com/md/semester_7/distributed_system/chapter-3

## Question

What do you mean by DOS (Distributed Operating System)? Briefly explain the monolithic and microkernel architectures of operating system.

## Short answer

A distributed operating system manages multiple computers to appear as one. Monolithic kernels contain all services in a single kernel-mode program, fast but rigid. Microkernels minimize the kernel to IPC, scheduling, and memory, running other services as user-level servers, offering modularity and distribution support with message passing overhead.

## Answer

#### Distributed operating system (DOS)
A **distributed operating system** is an operating system that manages a collection of independent computers and makes them appear to the user as a single computer (uniprocessor view). It controls all the resources, schedules processes on any node, and provides transparency, a global file system and global IPC. Examples: Amoeba, Mach, Sprite.

#### Monolithic kernel
All OS services (process, memory, file and device management, networking) are in one large kernel running in kernel mode, communicating by direct procedure calls. It is fast but big, rigid and error-prone. Examples: UNIX, Linux.

#### Microkernel
The kernel contains only a minimal set (IPC, address spaces, thread scheduling, interrupt handling). Other services run as user-level servers and use message passing.

```text
 Monolithic:            Microkernel:
 [App]                  [App] [FS] [Net] [Mem mgr]
 [ Big kernel:           ---- message passing ----
   FS,Net,MM,Drivers ]  [ Microkernel: IPC,sched ]
 Hardware               Hardware
```

| Point | Monolithic kernel | Microkernel |
|---|---|---|
| Structure | All OS services (file system, memory, scheduling, drivers, networking) in one large kernel in kernel space | Only minimum functions (IPC, basic scheduling, low level memory, interrupts) in kernel |
| Other services | Part of kernel | Run as user-level servers |
| Communication | Direct procedure calls (fast) | Message passing between servers (slower) |
| Size | Large | Small |
| Reliability | A bug in one module can crash the system | A server failure does not crash the kernel |
| Flexibility, extensibility | Hard; needs recompilation | Easy; add/replace servers |
| Examples | UNIX, Linux, MS-DOS | Mach, Amoeba, Chorus, QNX |

## Check yourself

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

1. What is a distributed operating system?
   A. A network protocol suite
   B. An OS that runs on one machine only
   C. A collection of unrelated OSs
   D. An OS managing independent computers so they appear as a single computer
   Answer: D. It gives a uniprocessor view with transparency, global file system and IPC. Examples: Amoeba, Mach. (Key point: DOS)

2. How do parts of a monolithic kernel communicate?
   A. Email
   B. Network messages between user servers
   C. Direct procedure calls
   D. Remote objects only
   Answer: C. That makes it fast, but big and rigid. (Key point: Monolithic IPC)

3. Where do file and network services run in a microkernel system?
   A. Inside the kernel
   B. As user-level server processes using message passing
   C. In hardware
   D. Only on the client
   Answer: B. A server failure then does not crash the kernel. (Key point: Microkernel services)

## Related in Distributed System

- [Short note: Monolithic and microkernel](https://www.bctengineer.com/question.md?key=semester_7%2Fdistributed_system%3Amonolithic-microkernel-note) — Distributed System, chapter 3, asked 4×
- [Microkernel vs monolithic kernel](https://www.bctengineer.com/question.md?key=semester_7%2Fdistributed_system%3Amicrokernel-advantages) — Distributed System, chapter 3
- [Why NOS preferred over DOS](https://www.bctengineer.com/question.md?key=semester_7%2Fdistributed_system%3Anos-vs-dos-realization) — Distributed System, chapter 3, asked 2×
- [Operating system layers](https://www.bctengineer.com/question.md?key=semester_7%2Fdistributed_system%3Aos-layers) — Distributed System, chapter 3
- [Autonomous vs distributed system](https://www.bctengineer.com/question.md?key=semester_7%2Fdistributed_system%3Aautonomous-vs-distributed) — Distributed System, chapter 1
- [Models of distributed system](https://www.bctengineer.com/question.md?key=semester_7%2Fdistributed_system%3Amodels-of-ds) — Distributed System, chapter 1

## Related in other subjects

- [System call; monolithic and VM architecture](https://www.bctengineer.com/question.md?key=semester_6%2Foperating_system%3Asystem-call-architecture) — Operating System, chapter 1
- [Functions of OS and microkernel](https://www.bctengineer.com/question.md?key=semester_6%2Foperating_system%3Aos-functions-microkernel) — Operating System, chapter 1
- [Features of a typical operating system](https://www.bctengineer.com/question.md?key=semester_4%2Fmicroprocessor%3Afeatures-of-operating-system) — Microprocessor, chapter 6, asked 3×
- [Monolithic vs micro-kernel structure](https://www.bctengineer.com/question.md?key=semester_6%2Foperating_system%3Amonolithic-vs-microkernel) — Operating System, chapter 1