Chp 1 - Introduction

Question 1

What is an OS?

Answer 1

An OS is a program that acts as an intermediary between a user of a computer and the computer hardware

Question 2

What is the goal of an OS?

Answer 2

Execute user programs, make the comp. system easy to use, utilize hardware efficiently

Question 3

Name the components of a computer system

Answer 3

Hardware ↔ OS ↔ Applications ↔ Users (↔ = ‘uses’)

Question 4

What are the OS’s main responsibilities?

Answer 4

◦ Resource allocator: decides between conflicting requests for efficient and fair resource use
◦ Control program: controls execution of programs to prevent errors and improper use of computer

Question 5

What is the Kernel?

Answer 5

the one program running at all times on the computer

Question 6

What is the bootstrap program?

Answer 6

loaded at power-up or reboot

Question 7

Where is the bootstrap program stored?

Answer 7

Stored in ROM or EPROM (known as firmware), Initializes all aspects of system, loads OS kernel and starts execution

Question 8

Can I/O and CPU execute concurrently?

Answer 8

yes

Question 9

What do Device Controllers do?

Answer 9

Device controllers inform CPU that it is finished w/ operation by causing an interrupt
◦
Interrupt transfers control to the interrupt service routine generally, through the interrupt vector, which contains the addresses of all the service routines

Incoming interrupts are disabled while another interrupt is being processed

Trap is a software generated interrupt caused by error or user request

OS determines which type of interrupt has occurred by polling or the vectored interrupt system

Question 10

What is a system call?

Answer 10

request to the operating system to allow user to wait for I/O completion

Question 11

Device-status table

Answer 11

contains entry for each I/O device indicating its type, address, and state
◦ OS indexes into the I/O device table to determine device status and to modify the table entry to include
interrupt

Question 12

Describe storage structure

Answer 12

Main memory – random access, volatile

Secondary storage – extension of main memory That provides large non-volatile storage

Disk – divided into tracks which are subdivided into sectors. Disk controller determines logical interaction
between the device and the computer.

Question 13

what is caching?

Answer 13

copying information into faster storage system

Question 14

Describe multiprocessor systems

Answer 14

Increased throughput, economy of
scale, increased reliability

Can be asymmetric or symmetric

Clustered systems – Linked multiprocessor systems

Question 15

What does multiprogramming do?

Answer 15

Provides efficiency via job scheduling

When OS has to wait (ex: for I/O), switches to another job

Question 16

what is timesharing?

Answer 16

– CPU switches jobs so frequently that each user

can interact with each job while it is running (interactive computing)

Question 17

What is a dual-mode os?

Answer 17

operation allows OS to protect itself and other system components – User mode and kernel mode
◦ Some instructions are only executable in kernel mode, these are privileged

Question 18

How may program counters does a single and multi-threaded process have?

Answer 18

• Single-threaded processes have one program counter, multi-threaded processes have one PC per thread

Question 19

What is process protection?

Answer 19

mechanism for controlling access of processes or users to resources defined by the OS