Test 1

Question 1

Operating System

Answer 1

software that runs on the bare hardware of a computer and provides essential support for users to develop and use applications in the most efficient and safe manner

Question 2

Multiprogramming

Answer 2

a technique that keeps several programs to maximize the use of the CPU and other resources.

Question 3

Time Sharing ( Multitasking )

Answer 3

an extension of multiprogramming where the CPU is switched periodically among all active computation to guarantee acceptable response time to each user

Question 4

Is multiprogramming without interrupts?

Answer 4

Multiprogramming does not require interrupts. A context switch happens whenever a computation terminates or blocks to wait for I/O. The termination of an I/O operation can be detected periodically checking the device status.

Question 5

Is time-sharing possible without interrupts?

Answer 5

Time-sharing requires a periodic interrupt to prevent long-running computations from monopolizing the CPU and thus delaying other computations for unpredictable amounts of time.

Question 6

What do multiprogramming and time-sharing have in common?
What are the differences between the two?

Answer 6

Multiprogramming allows multiple programs to be active in memory simutaneously. While one is waiting for I/O completion or some other event, another can run on the CPU. The main objective is to increase CPU and device utilization.

Question 7

Kernel

Answer 7

an os is the minimal set of functions necessary to manage the system resources safely and efficiently.

Question 8

Privileged Instruction

Answer 8

performs critical operations that access I/O devices and the CPU’s status and control registers. Thus only the OS Kernel is allowed to execute privileged instructions

Question 9

Kernel Mode

Answer 9

The CPU state where both privilege and non-privilege instruction may be used

Question 10

User Mode

Answer 10

the CPU state where non-privilege instructions may be used. Any attempt to execute a privilege instruction in user mode automatically transfer control to the Kernel

Question 11

OS Shell

Answer 11

a command interpreter that accepts and interprets textual commands issued by the user

Question 12

Interrupt

Answer 12

an event that diverts the current execution of a program to a predefined location in the kernel in other to respond to an event. An interrupt is triggered by a hardware signal sent to the cpu from an external device

Question 13

Most Common interrupts

Answer 13

Signal to O/S the completion of an I/O operation. The interrupt is generated by the I/O device.
Implement time-sharing by periodically switching the CPU among multiple concurrent computations. THe interrupt generated by a countdown timer

Question 14

Trap

Answer 14

is an interrupt triggered by the currently executing instruction

Question 15

Interrupt handler

Answer 15

is kernel function invoked whenever an interrupt occurs, that determines that cause of the interrupt and invokes the appropriate kernel function to provide the response

Question 16

Process

Answer 16

is an instance of a program being executed by an O/S

Question 17

Process Control Block (PCB)

Answer 17

a data structure that holds info for a process, including the current instruction address, the execution stack the set of resources used by the process, and the program being executed.

Question 18

Context Switch

Answer 18

is the transfer of control from one process to another

Question 19

New -> ready -> suspend -> blocked -> suspend

Answer 19

invalid process that went from ready to suspend must return rather than blocked

Question 20

suspend -> blocked -> suspend -> clocked -> ready -> running

Answer 20

a suspend process goes back to a blocked state. Next, the process may be suspended again and later return back to the blocked state. When the resource becomes available, the process transition to ready. Finally from ready the process may go into runnning

Question 21

Multiprogramming generally improves CPU utilization

Question 21

Multiprogramming generally improves CPU utilization and throughput

Answer 21

True

Question 22

The main objective of time-sharing is to improve resource utilization

Answer 22

False

Question 23

Multiprogramming and time-sharing are not used togheter

Answer 23

False

Question 24

The use of time-sharing will

Answer 24

guarantee a reasonable response to each computation

Question 25

Kernel Functions may be invoked by

Answer 25

any program

Question 26

Privilege instructions may be executed by

Answer 26

only the kernel

Question 27

An application that needs to access an I/O device could not be written without

Answer 27

kernel functions

Question 28

The kernel can execute ____instructions

Answer 28

Both privilege and non privelge

Question 29

A system call is a

Answer 29

library function

Question 30

A supervisor call is a

Answer 30

privilege instruction

Question 31

A supervisor call can be executed

Answer 31

by any program

Question 32

Changing the mode bit of the CPU _____ can only be done by privileged instruction

Answer 32

from user mode to kernel mode

Question 33

An OS uses PCB to represent a process.

Answer 33

True

Question 34

The PCB is created by the process when execution start

Answer 34

FALSE

Question 35

The PCB becomes part of the program being executed by a process

Answer 35

False

Question 36

Two processes can be executing the same program

Answer 36

True

Question 37

The transition ( ready -> running ) of a process p is called

Answer 37

the OS

Question 38

The transition (running -> blocked) of a process p is caused by

Answer 38

the process p itself

Question 39

The transition (running -> ready) of a process p is caused

Answer 39

the OS

Question 40

The transition (blocked -> ready) of process p is caused by

Answer 40

some other process