Operating Systems Overview

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Questions and Answers

What is an operating system?

A set of programs that manages the operations of the computer for the user. It acts as a bridge between the user and the computer's hardware.

Where is the operating system held?

In permanent storage, such as a hard disk.

How is the operating system started up?

A small program called the loader is held in ROM, which loads the operating system from storage into RAM.

What are the functions of an operating system?

It provides a user interface, memory management, interrupt service routines, processor scheduling, backing store management, and management of all input and output. Signup and view all the answers

Name 2 memory management techniques used by the operating system.

Paging and Segmentation. Signup and view all the answers

Describe paging.

Memory is divided into fixed size pages of 4Kb each. A process in memory may be held in several non-contiguous pages. Signup and view all the answers

What is a page table?

A page table uses mapping to store a link between the physical memory address and the logical address space of each process. Signup and view all the answers

What is segmentation?

Logical division of address space into varying length segments which depend on the program structure. Signup and view all the answers

What is virtual memory?

As RAM gets full, the OS may swap pages of temporarily inactive jobs out to disk, using secondary storage as an extension of memory. Signup and view all the answers

What is disk thrashing?

Insufficient memory causing continuous swapping of pages in and out of RAM, leading to performance dips. Signup and view all the answers

What is an interrupt?

A signal from a program, hardware device or clock to the CPU to get attention. Signup and view all the answers

What happens when the CPU receives an interrupt?

It suspends the running program, disables lower priority interrupts, stores values onto the system stack, calls an Interrupt Service Routine, and resumes after servicing the interrupt. Signup and view all the answers

Give 3 examples of interrupts in descending order of priority.

<ol> <li>Power-fail interrupt 2) Clock interrupt 3) An I/O device sends a signal requesting service.</li> </ol> Signup and view all the answers

Study Notes

Definition of an Operating System

A collection of programs that manages computer operations for users.
Acts as a bridge facilitating user interaction with hardware.

Location of the Operating System

Stored in permanent storage, typically on a hard disk.

Startup Process

Initiated by a small program known as the loader, located in ROM.
Loader transfers instructions to load the OS from permanent storage to RAM when the computer powers on.

Functions of an Operating System

Provides a user interface for interaction.
Manages memory allocation and usage.
Executes interrupt service routines to handle events.
Oversees processor scheduling to maximize efficiency.
Manages backing store for file storage.
Controls input and output operations across devices.

Memory Management Techniques

Paging: Memory divided into fixed-size pages (usually 4KB); allows non-contiguous allocation.
Segmentation: Divides address space into variable-length segments based on program structure.

Paging Details

Each process can utilize multiple non-contiguous pages stored in memory.

Page Table

A mapping system that connects physical memory addresses to logical address spaces for each process.

Segmentation Characteristics

Allocates memory in segments that vary in length, depending on the program's structure.
Allows partial loading of programs into memory.

Virtual Memory Functionality

Extends memory capacity by swapping inactive job pages to disk when RAM is full, allowing secondary storage to function as additional memory.

Disk Thrashing Phenomenon

Occurs with insufficient memory, leading to excessive swapping of pages between RAM and disk, negatively impacting system performance.

Interrupt Mechanisms

A signal from software, hardware, or internal clock indicating the CPU needs attention.
Examples include completion of application programs or requests for OS services.

CPU Response to Interrupts

Suspends current program execution and disables lower priority interrupts.
Stores program counter (PC) and register values on the system stack before invoking an Interrupt Service Routine (ISR).
Upon servicing the interrupt, original register values are restored, allowing the program to continue from where it was interrupted.

Examples of Interrupts in Priority Order

Power-fail interrupt (highest priority).
Clock interrupt (medium priority).
I/O device signal for requesting service or indicating end of operation (lowest priority).

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Description

This quiz covers the definition, location, startup process, and functions of operating systems. It also explores memory management techniques such as paging and segmentation. Test your knowledge on how operating systems interact with hardware and manage system resources.