OS1 introduction

Question 1

What is an operating system

Answer 1

• first program that hardware runs
• program that runs other programs
• acts as middle man between user and hardware
• coordinates use of hardware amongst different programs

Question 2

goals of the OS (3)

Answer 2

execute user programs, make computer systems and convenient to use, use hardware efficiently

Question 3

Explain the analogy of the OS being a government

Answer 3

protects user from each other - one cannot overwrite another

allocates resources efficiently and fairly

Question 4

Key function of the OS

Answer 4

provide computational environment within which other programs can do useful work

Question 5

Name and explain the two different OS views from a systems perspective

Answer 5

First view - resource allocator that manages system resources and decides between conflicting requests for efficient and fair resource use
Second - control program that controls execution of programs - prevent errors and improper use of computer

Question 6

Explain how the OS is an abstraction f the workings of a computer system. Give an example

Answer 6

OS is an interface between users and hardware.

OS can share resources between user programs and system applications thus is able to concurrently process the running of multiple programs.

Question 7

What is the OS user level?

Answer 7

part of the OS that the user directly interacts with - consists of programs that the user creates or imports, libraries, system application programs

Question 8

OS kernel level

Answer 8

Core of the OS, kept in main memory at all times.
Ensures that essential OS operations are kept running
Runs device drivers - enable OS to interact with hardware

Question 9

name 2 essential OS operations

Answer 9

File management and storage in secondary memory (hard-disk)storage

process control (scheduling and executing programs) to run in main memory and to allocate each process appropriate computational resources

Question 10

OS hardware level

Answer 10

Physical devices that the OS uses e.g. CPU, HDD, keyboards etc

Question 11

Why have abstractions

Answer 11

Reduce complexity expected from user

reduce program design complexity

Question 12

Name 3 examples of abstraction

Answer 12

User
Disk
Process
File

Question 13

What is multi-programming abstraction

Answer 13

rapid switching between the running of programs and keeping all programs partially loaded into memory

Question 14

Issues with file abstraction

Answer 14

files need unique names and addresses in phys mem
Efficiently organized in phys mem for quick retrieval
Eventually more files than phys mem space

Question 15

Why is it not possible to store programs and data in main memory permanently? What is a fix for this?

Answer 15

Too small
Volatile (loses contents when power off)

secondary storage (typically magnetic HDD)

Question 16

Virtual memory allows the execution…

Answer 16

of programs that are not completely in memory

Question 17

What does virtual memory allow programs to do?

Answer 17

use more memory than available in phys memory, share files and data easily (implements shared memory)

by abstracting main memory to large, uniform memory array that uses second storage to temporary hold programs that must eventually be put into main mem for execution

Question 18

Benefits of using VMemory

Answer 18

• programs no longer constrained by amount of phys mem
• each user program takes less physical memory: more programs can run at same time therefore increasing CPU use and program throughput (with no increase in run time)

Question 19

What is Multiplexing (OS - RAM)

Answer 19

resource abstraction means that these N programs use virtual memory to share the space of limited main memory. This sharing of main memory by multiple programs is known as multiplexing

Question 20

Explain how multiplexing occurs on the CPU

Answer 20

CPU - can only execute one program at a time but N programs run concurrently on OS. N programs execute in chunks with rapid switching between them

Question 21

Explain how the OS is a type of virtual machine

Answer 21

Each process seems to execute on own processor - OS mandates that resources of physical machine must be shared.

Question 22

Function of a VMachine

Answer 22

provides interface to application layer

Question 23

Purpose of the Java VMachine

Answer 23

allows java code to be portable between different OS and hardware
enables a computer to run Java programs that are compiled into Javabyte-code
Abstraction so that java devs dont need to worry about underlying hardware platform and OS

Question 24

Concurrency vs parallelism

Answer 24

Concurrency - same cpu multiple programs at same time

Parallel - multiple programs, multiple CPU at same time

Question 25

Key problem with concurrency at OS level

Answer 25

multiple processes must safely interact (e.g. not over-write each other)