--- title: "Functions of OS and microkernel" subject: "Operating System" chapter: 1 key: "semester_6/operating_system:os-functions-microkernel" source: https://www.bctengineer.com/q/semester_6/operating_system/os-functions-microkernel site: BCT Engineering --- # Functions of OS and microkernel Operating System · Chapter 1: Introduction to Operating System - Asked in: 2068 Bhadra, 3+5 marks - Video: [Structures of Operating System](https://www.youtube.com/watch?v=XXPBl20J22w) — Neso Academy - Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14 - Page: https://www.bctengineer.com/q/semester_6/operating_system/os-functions-microkernel - Whole chapter: https://www.bctengineer.com/md/semester_6/operating_system/chapter-1 ## Question What are the functions of an operating system? Explain about microkernel. ## Short answer OS functions include process, memory, file, and I/O management, protection, and user interface. A microkernel keeps only essential services (IPC, scheduling, basic memory) in kernel mode; other services like file systems and drivers run as user-mode servers communicating via message passing. ## Answer #### Functions of an operating system 1. **Process management**: creation, scheduling, synchronization, communication and termination of processes. 2. **Memory management**: allocation, protection, swapping, paging and virtual memory. 3. **File-system management**: files and directories, access control, storage allocation. 4. **I/O (device) management**: device drivers, buffering, spooling and disk scheduling. 5. **Protection and security**: authentication and access control for resources. 6. **User interface**: shell or GUI, error handling and resource accounting. #### Microkernel A **microkernel** is an OS design in which only the minimum essential services run in kernel mode, and everything else runs as ordinary user-mode server processes. The microkernel keeps only: - low-level **address-space management** (basic memory handling), - **process/thread management and scheduling**, and - **inter-process communication (IPC)** by message passing. The file system, device drivers, networking and memory pagers run as separate **servers** in user space. A client requests a service by sending a message to the microkernel, which passes it to the right server and returns the reply. ```text User mode: +------+ +--------+ +---------+ +-----+ | File | | Device | | Network | | App | | srv | | driver | | server | | | +--+---+ +---+----+ +----+----+ +--+--+ | | | | ---+---------+-----------+---------+--- Kernel mode: +------------------------------------+ | Microkernel: IPC, scheduling, | | basic memory management | +------------------------------------+ | Hardware | +------------------------------------+ ``` **Advantages**: small, easy to port and extend; more reliable and secure because a failing server does not crash the kernel; servers can be added or replaced without recompiling the kernel. **Disadvantage**: slower than a monolithic kernel because of repeated message passing and mode switches. Examples: Mach, QNX, MINIX 3. ## Check yourself The answer's key points as multiple-choice questions, with the correct option and why. 1. Which services does a microkernel keep in kernel mode? A. Address-space management, process/thread scheduling and IPC by message passing B. File system, device drivers and networking C. Only the user interface D. All device drivers and the shell Answer: A. Only minimum essentials stay in the kernel; the rest run as user-mode servers. (Key point: Microkernel contents) 2. Where do the file system and device drivers run in a microkernel OS? A. Inside the kernel as compiled-in modules B. As separate server processes in user mode C. In the hardware controller D. In the BIOS Answer: B. They run as user-space servers and clients reach them by messages through the microkernel. (Key point: Servers in user space) 3. Why is a microkernel more reliable than a monolithic kernel? A. It has more code running in kernel mode B. It avoids using message passing C. A failing server does not crash the kernel D. It never needs scheduling Answer: C. Servers are in user space, so their failure is isolated from the kernel. (Key point: Reliability advantage) 4. What is the main disadvantage of a microkernel? A. It cannot be ported to other hardware B. Servers cannot be replaced without recompiling the kernel C. It has a very large trusted code base D. Slower because of repeated message passing and mode switches Answer: D. Each service request involves messages and mode switches, costing speed. (Key point: Microkernel disadvantage) ## Related in Operating System - [What is an OS; its functions](https://www.bctengineer.com/question.md?key=semester_6%2Foperating_system%3Aos-functions-definition) — Operating System, chapter 1, asked 2× - [OS abstraction, extended machine, system call](https://www.bctengineer.com/question.md?key=semester_6%2Foperating_system%3Aos-abstraction-system-call) — Operating System, chapter 1 - [OS as virtual machine; functions](https://www.bctengineer.com/question.md?key=semester_6%2Foperating_system%3Aos-virtual-machine-functions) — Operating System, chapter 1 - [OS definition and types of OS](https://www.bctengineer.com/question.md?key=semester_6%2Foperating_system%3Aos-definition-types) — Operating System, chapter 1 - [Layered vs monolithic OS structure](https://www.bctengineer.com/question.md?key=semester_6%2Foperating_system%3Alayered-vs-monolithic) — Operating System, chapter 1 - [Pipe, shell; OS as resource manager](https://www.bctengineer.com/question.md?key=semester_6%2Foperating_system%3Apipe-shell-resource-manager) — Operating System, chapter 1 ## Related in other subjects - [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× - [DOS; monolithic and microkernel](https://www.bctengineer.com/question.md?key=semester_7%2Fdistributed_system%3Ados-monolithic-microkernel) — Distributed System, chapter 3 - [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× - [Operating system layers](https://www.bctengineer.com/question.md?key=semester_7%2Fdistributed_system%3Aos-layers) — Distributed System, chapter 3