--- title: "Supervisor call; batch, RT, time sharing" subject: "Operating System" chapter: 1 key: "semester_6/operating_system:supervisor-call-os-types" source: https://www.bctengineer.com/q/semester_6/operating_system/supervisor-call-os-types site: BCT Engineering --- # Supervisor call; batch, RT, time sharing Operating System · Chapter 1: Introduction to Operating System - Asked in: 2071 Bhadra, 2+8 marks - Video: [Types of Operating System | Batch, Real-time, Distributed, Network, Time-sharing Operating System](https://www.youtube.com/watch?v=Ij71sDmmKpc) — Learn Coding - Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14 - Page: https://www.bctengineer.com/q/semester_6/operating_system/supervisor-call-os-types - Whole chapter: https://www.bctengineer.com/md/semester_6/operating_system/chapter-1 ## Question What is the role of supervisor call in an operating system? Write down the major differences between the following types of operating system: a) Batch system b) Interactive system c) Real time system d) Time sharing system. ## Short answer A supervisor call (SVC) is a system call causing a trap to kernel mode, enabling controlled access to privileged services. Batch runs jobs sequentially with no interaction for high throughput. Interactive provides direct user dialogue with short response. Real-time guarantees bounded deadlines via preemptive scheduling. Time-sharing shares CPU among multiple users in small time quantums. ## Answer #### Role of supervisor call A **supervisor call (SVC)**, also called a system call, is the instruction by which a user program asks the OS (supervisor) to perform a privileged service such as I/O, memory allocation or process creation. It causes a trap that switches the CPU from **user mode to supervisor (kernel) mode** and passes control to the OS routine, then returns to user mode. Its role is to give programs controlled access to protected operations, so that the OS can check the request and protect the system and other users. #### Differences between the types | Basis | Batch | Interactive | Real-time | Time-sharing | |---|---|---|---|---| | Aim | Maximise throughput / CPU use | Quick response to a user's commands | Meet deadlines | Share CPU among many users fairly | | User interaction | None while the job runs | Direct, continuous | Mostly with sensors/devices | Many users at terminals at once | | Job handling | Jobs grouped in batches, run in sequence | Commands processed as typed | Event/interrupt driven tasks | CPU switched in small time slices | | Response time | Long (hours) | Short (seconds) | Guaranteed, very short and bounded | Short (about 1 s) | | Scheduling | FCFS / SJF | Round robin / priority | Priority-based, preemptive (RM, EDF) | Round robin | | CPU idle | Possible during I/O | Reduced | Kept ready for events | Minimal (multiprogramming) | | Examples | Payroll, bank statements | Word processor, PC OS | Missile control, robotics, VxWorks | UNIX, Multics | ## Check yourself The answer's key points as multiple-choice questions, with the correct option and why. 1. What does a supervisor call do? A. Lets the user program execute privileged instructions directly B. Traps from user mode to supervisor (kernel) mode so the OS can perform a privileged service after checking the request C. Shuts down the OS D. Switches kernel to user mode permanently Answer: B. It gives controlled access to protected operations. (Key point: Supervisor call role) 2. How does response time compare? A. Batch is short, interactive is long B. Both are identical C. Batch is long (hours), interactive is short (seconds) D. Batch is bounded to milliseconds Answer: C. Batch aims at throughput; interactive at quick response. (Key point: Batch vs interactive) 3. What is the aim of a real-time system? A. Maximise throughput only B. Run in batches C. Share CPU only fairly among many users D. Meet deadlines with guaranteed, bounded response Answer: D. Real-time uses priority preemptive scheduling (RM, EDF). (Key point: Real-time aim) ## Related in Operating System - [Batch vs interactive OS suitability](https://www.bctengineer.com/question.md?key=semester_6%2Foperating_system%3Abatch-interactive-os-applications) — Operating System, chapter 1 - [Preemptive vs non-preemptive; real-time scheduling](https://www.bctengineer.com/question.md?key=semester_6%2Foperating_system%3Apreemptive-nonpreemptive-realtime) — Operating System, chapter 2 - [Rate Monotonic real-time schedule](https://www.bctengineer.com/question.md?key=semester_6%2Foperating_system%3Arate-monotonic-schedule) — Operating System, chapter 2 - [Real-time scheduling; two-processor numerical](https://www.bctengineer.com/question.md?key=semester_6%2Foperating_system%3Arealtime-two-processor-fcfs-sjf-priority-rr) — Operating System, chapter 2 - [System call; monolithic and VM architecture](https://www.bctengineer.com/question.md?key=semester_6%2Foperating_system%3Asystem-call-architecture) — Operating System, chapter 1 - [System call; read() execution](https://www.bctengineer.com/question.md?key=semester_6%2Foperating_system%3Asystem-call-read-example) — Operating System, chapter 1 ## Related in other subjects - [Real-time system and real-time OS components](https://www.bctengineer.com/question.md?key=semester_5%2Fsoftware_engineering%3Areal-time-os) — Software Engineering, chapter 4 - [Basic functions of real-time kernel](https://www.bctengineer.com/question.md?key=semester_6%2Fembedded_system%3Areal-time-kernel-functions) — Embedded System, chapter 6, asked 2× - [Real-time versus ordinary software and OS; data acquisition](https://www.bctengineer.com/question.md?key=semester_5%2Fsoftware_engineering%3Areal-time-vs-non-real-time) — Software Engineering, chapter 4 - [General OS versus real-time OS](https://www.bctengineer.com/question.md?key=semester_5%2Fsoftware_engineering%3Ageneral-os-vs-rtos) — Software Engineering, chapter 4