---
title: "OS as resource manager and extended machine"
subject: "Operating System"
chapter: 1
key: "semester_6/operating_system:os-resource-manager-extended-machine"
source: https://www.bctengineer.com/q/semester_6/operating_system/os-resource-manager-extended-machine
site: BCT Engineering
---

# OS as resource manager and extended machine

Operating System · Chapter 1: Introduction to Operating System

- Asked in: year not given
- Video: [#part-2#Explain operating system as an Extended machine and as a Resource manager| #unit1 #msc #bsc](https://www.youtube.com/watch?v=4-3Nrv_JJIk) — kitu Fogat
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_6/operating_system/os-resource-manager-extended-machine
- Whole chapter: https://www.bctengineer.com/md/semester_6/operating_system/chapter-1

## Question

Explain operating system as a resource manager and as an extended machine.

## Short answer

As resource manager, OS allocates CPU, memory, I/O among programs via time and space multiplexing. As extended machine, it hides hardware complexity, providing abstractions like files and processes via system calls, making programming easier and portable.

## Answer

#### Operating system as a resource manager

A computer system has many resources: CPU, memory, disks, I/O devices, files and network. Several programs and users demand them at the same time. The OS is the **resource manager**: it keeps track of the resources, decides who gets what, when and how much, grants and reclaims them, and settles conflicting requests so that resources are used efficiently and fairly.

Resources are shared in two ways:
- **Time multiplexing**: users take turns using the resource (CPU, printer).
- **Space multiplexing**: each user gets a part of the resource at the same time (memory, disk).

Example: when two programs print at the same time, the OS queues (spools) the jobs so that their outputs do not mix. Besides allocation, the OS provides protection and accounting. This is the **bottom-up** view of the OS: it manages the hardware.

#### Operating system as an extended machine

Raw hardware is complex and difficult to program. The OS hides its details and presents an easier, abstract machine (the **extended or virtual machine**). Instead of dealing with disk-controller registers, a programmer uses abstractions like **files, processes and address spaces** through system calls such as `open` and `read`. This is the **top-down** view: it makes the machine convenient and portable for application programmers.

```text
 Application programs
 ---------------------  Extended machine view
 Operating system      (files, processes, sockets)
 ---------------------  Resource manager view
 Hardware               (CPU, memory, disks, I/O)
```

Therefore the OS has a dual role: it extends the machine for the user and manages the machine's resources.

## Check yourself

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

1. What does the OS do as resource manager?
   A. Hides hardware behind abstractions only
   B. Only compiles code
   C. Only draws windows
   D. Decides who gets what, when and how much, grants and reclaims resources and settles conflicts
   Answer: D. It manages the hardware efficiently and fairly. (Key point: Resource manager)

2. Why does the OS spool two programs' prints?
   A. So their outputs do not mix
   B. To speed up the CPU
   C. To delete the files
   D. To avoid using the printer
   Answer: A. Queueing serialises access to the printer. (Key point: Spooling)

3. Which view is top-down?
   A. OS as resource manager
   B. OS as extended machine, giving convenient abstractions to programmers
   C. OS as a hardware component
   D. OS as a compiler
   Answer: B. Resource manager is bottom-up; extended machine is top-down. (Key point: Top-down vs bottom-up)

## Related in Operating System

- [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
- [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
- [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 as virtual machine; functions](https://www.bctengineer.com/question.md?key=semester_6%2Foperating_system%3Aos-virtual-machine-functions) — Operating System, chapter 1