Chapter 1

Question 1

What is an Operating System?

Answer 1

A program that acts as an intermediary between a user of a computer and the computer hardware.

Question 2

Goals of Operating System?

Answer 2

• Execute user programs and make solving user problems easier
• Make the computer system convenient to use
• Use the computer hardware in an efficient manner

Question 3

4 Components of Computer System

Answer 3

Hardware
Operating System
Application Programs
Users

Question 4

Operating System Definition

Answer 4

OS is a resource allocator

OS is a control program

Question 5

What is Resource Allocator?

Answer 5

Manages all resources

Decides between conflicting requests for efficient and fair resource use

Question 6

What is a control program?

Answer 6

Controls execution of programs to prevent errors and improper use of the computer

Question 7

What is Bootstrap Program?

Answer 7

Bootstrap program is loaded at power-up or reboot

• Typically stored in ROM or EPROM, generally known as firmware
• Initializes all aspects of system
• Loads operating system kernel and start execution

Question 8

Computer System Organization

Answer 8

Computer-System operation

• One r more CPUs, device controllers connect through common bus providing access to shared memory
• Concurrent execution of CPUs and devices competing for memory cycles

Question 9

Operating System Structure

Answer 9

• Multiprogramming

- Timesharing

Question 10

What is Multiprogramming?

Answer 10

Also known as Batch System needed for effiency

• Single user cannot keep CPU and I/O devices busy at all times
• A subset of total jobs in system is kept in memory
• One job selected and run via job scheduling
• When it has to wait, OS switches to another job

Question 11

What is Timesharing?

Answer 11

Known as Multitasking is logical extension in which CPU switches jobs so frequently that users can interact with each job while it is running, creating, interactive computing

Question 12

Timesharing attributes?

Answer 12

• Response time should be less than 1 second
• Each user has at least one program executing in memory (process)
• If several jobs ready to run at the same time (CPU scheduling)
• If processes don’t fit in memory, swapping moves them in and out to run.
• Virtual memory allows execution of processes not completely in memory.

Question 13

Operating-System Operations

Answer 13

Interrupt Driven (hardware and software)
Software Interrupt (exception or trap)
Dual-mode
Increasingly CPUs support multi-mode operations

Question 14

What is Dual-mode?

Answer 14

Dual-mode operation allows OS to protect itself and other system components

• User mode and Kernel Mode
• Mode bit provided by hardware

Question 15

Transition from User to Kernel Mode

Answer 15

Timer to prevent infinite loop / process hogging resources

• Timer is set to interrupt the computer after some time period
• Keep a counter that is decremented by the physical clock.
• Operating system set the counter
• When the counter zero generate an interrupt
• Set up before scheduling process to regain control or terminate program that exceeds allotted time.

Question 16

Process Management & Synchronization

Answer 16

A process is a program in execution. It is a unit of work within the system, Program is a passive entity, process is an active entity.

Process needs resources to accomplish its task

• CPU, memory, I/O, files
• Initialization data

Process termination requires reclaim of any reusable resources