--- title: "OS definition and types of OS" subject: "Operating System" chapter: 1 key: "semester_6/operating_system:os-definition-types" source: https://www.bctengineer.com/q/semester_6/operating_system/os-definition-types site: BCT Engineering --- # OS definition and types of OS Operating System · Chapter 1: Introduction to Operating System - Asked in: 2071 Magh, 1+4 marks; year not given - Video: [Introduction To Operating System | OS Functions , Features And Types](https://www.youtube.com/watch?v=dpnYzKATBKA) — Learn Computer Science - Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14 - Page: https://www.bctengineer.com/q/semester_6/operating_system/os-definition-types - Whole chapter: https://www.bctengineer.com/md/semester_6/operating_system/chapter-1 ## Question What is an operating system? Briefly mention the types of operating system. Distinguish between kernel and micro-kernel. ## Short answer An operating system manages hardware resources and provides services for users and applications. Types include batch, multiprogramming, time-sharing, multiprocessor, distributed, and real-time OS. A monolithic kernel runs all services in kernel mode; a microkernel runs only IPC, scheduling, and basic memory in kernel mode with other services as user-mode servers. ## Answer An **operating system** is system software that manages hardware resources and provides services and a convenient interface for users and application programs (for example Windows, Linux, Android). #### Types of operating systems - **Batch OS**: similar jobs are collected into a batch and run one after another without user interaction. - **Multiprogramming OS**: several jobs are kept in memory and the CPU switches to another job when one waits for I/O, so the CPU stays busy. - **Time-sharing (multitasking) OS**: the CPU is switched quickly among users/processes using small time slices, so each user gets an interactive response (UNIX, Linux). - **Multiprocessor (parallel) OS**: manages a computer with more than one CPU sharing memory and I/O. - **Distributed OS**: manages a group of independent computers connected by a network and makes them appear as one system. - **Real-time OS**: guarantees a response within a fixed deadline (industrial control, missile systems). - **Network OS** and **embedded/mobile OS** are other types. #### Kernel vs micro-kernel | Basis | Kernel (monolithic) | Micro-kernel | |---|---|---| | Size | Large, all services inside | Very small, only essentials | | Services in kernel mode | File system, drivers, memory, networking | Only IPC, scheduling, basic memory | | Other services | Part of the kernel | User-mode server processes | | Speed | Faster (direct function calls) | Slower (message passing) | | Reliability | A bug in a driver can crash the system | A server failure does not crash the kernel | | Extending | Needs kernel recompile | Add or replace servers easily | | Examples | Traditional UNIX, Linux | Mach, QNX, MINIX 3 | ## Check yourself The answer's key points as multiple-choice questions, with the correct option and why. 1. What is the main idea of a multiprogramming OS? A. Keep several jobs in memory and switch the CPU to another job when one waits for I/O B. Run one job at a time without user interaction C. Guarantee response within a fixed deadline D. Make several computers appear as one Answer: A. Switching on I/O wait keeps the CPU busy. (Key point: Multiprogramming) 2. What distinguishes a real-time OS? A. It batches similar jobs overnight B. It guarantees a response within a fixed deadline C. It manages computers over a network as one system D. It only runs on a single user machine Answer: B. RTOS are used in industrial control and missile systems where deadlines matter. (Key point: Real-time OS) 3. What does a distributed OS do? A. Manages one computer with several CPUs sharing memory B. Runs jobs in batches C. Manages independent networked computers and makes them appear as one system D. Switches CPU among users with small time slices Answer: C. That describes distributed, as opposed to multiprocessor, systems. (Key point: Distributed OS) 4. Why is a monolithic kernel faster than a micro-kernel? A. It keeps fewer services in the kernel B. It runs services in user mode C. It uses separate servers for drivers D. Services use direct function calls instead of message passing Answer: D. Direct calls avoid message passing and mode switches. (Key point: Kernel vs microkernel speed) ## Related in Operating System - [Monolithic vs micro-kernel structure](https://www.bctengineer.com/question.md?key=semester_6%2Foperating_system%3Amonolithic-vs-microkernel) — Operating System, chapter 1 - [Extended machine, kernel, system call](https://www.bctengineer.com/question.md?key=semester_6%2Foperating_system%3Aextended-machine-kernel-syscall) — Operating System, chapter 1 - [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 - [Device controller vs kernel; DMA](https://www.bctengineer.com/question.md?key=semester_6%2Foperating_system%3Adevice-controller-vs-kernel-dma) — Operating System, chapter 6 - [Process vs thread; user and kernel threads](https://www.bctengineer.com/question.md?key=semester_6%2Foperating_system%3Aprocess-vs-thread-user-kernel-threads) — Operating System, chapter 2 - [OS as virtual machine; functions](https://www.bctengineer.com/question.md?key=semester_6%2Foperating_system%3Aos-virtual-machine-functions) — Operating System, chapter 1 ## Related in other subjects - [Importance of kernel OS in embedded](https://www.bctengineer.com/question.md?key=semester_6%2Fembedded_system%3Aimportance-of-kernel-os) — Embedded System, chapter 6 - [File system handling of kernel](https://www.bctengineer.com/question.md?key=semester_6%2Fembedded_system%3Akernel-file-system-handling) — Embedded System, chapter 6 - [Microkernel vs monolithic kernel](https://www.bctengineer.com/question.md?key=semester_7%2Fdistributed_system%3Amicrokernel-advantages) — 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×