1.2.1 Systems software - Gurjot

Question 1

what is an operating system

Answer 1

a collection of programs that work together in order to provide an interface between the user and the computer

Question 2

state some features that an operating system provides

Answer 2

• memory management
• file management
• utility software
• user interface

Question 3

what is paging

Answer 3

when memory is split up into equal sized sections (called pages). these can be swapped between main memory and hard disk as needed.

Question 4

what is segmentation

Answer 4

splitting up memory into logical sized divisions (called segment).

Question 5

what is virtual memory

Answer 5

using a section of hard drive to act as RAM when the space in the main memory in insufficient. sections currently not in use are moved into virtual memory through paging

Question 6

what are the issues with the 3 ways of memory management

Answer 6

it causes disk thrashing (when the computer freezes as pages are being swapped too frequently between hard disk and main memory.)

Question 7

what are interrupts

Answer 7

signals generated by software or hardware to indicate to the processor that a process needs attention

Question 8

describe the steps of the interrupt service routine

Answer 8

• Interrupt Request: Device signals the CPU
• Acknowledgement and Save Content: CPU finishes current task, saves state to the stack
• Identify and Execute ISR: CPU identifies interrupt source and runs ISR
• Restore and Resume: CPU restore saved context and resumes main program

Question 9

what is pre-emptive scheduling

Answer 9

jobs are actively made to start and stop by the operating system

Question 10

give examples of pre-emptive scheduling

Answer 10

• multi level feedback queues
• shortest time remaining
• round robin

Question 11

what is non pre-emptive scheduling

Answer 11

once a job is started, its left alone until completed

Question 12

give examples of non pre-emptive scheduling

Answer 12

• first come first served
• shortest job first

Question 13

describe round robin scheduling

Answer 13

each job is given a section of processor time, if not completed in the time, its put back in the queue.

Question 14

describe first come first served

Answer 14

jobs are processed in order of which entered the queue first

Question 15

describe multi level feedback queues

Answer 15

makes uses of multiple queues, ordered based on different priority.

Question 16

describe shortest job first

Answer 16

jobs processed in ordered according to the time required for completion, with the shortest at the front

Question 17

describe shortest time remaining

Answer 17

the queue storing jobs is ordered according for the time left for completion. if a new job enters the queue, its compared to the one being processed and is replaced with the one being replaced if it has a shorter completion time.

Question 18

what is processor starvation

Answer 18

when a process does not receive enough time in order to be completed.

Question 19

what scheduling algorithms are at risk of processor starvation

Answer 19

• shortest time remaining
• shortest job first

Question 20

describe a distributed operating system

Answer 20

an os run across multiple devices, so load is spread across multiple processors.

Question 21

describe an embedded os

Answer 21

built to perform a small range of specific tasks catered to a specific device

Question 22

describe a multi tasking os

Answer 22

enables user to carry out tasks seemingly simultaneously using time slicing

Question 23

describe a multi user os

Answer 23

makes use of a supercomputer , and scheduling algorithm to ensure time is shared fairly between jobs

Question 24

describe a real time os

Answer 24

designed to perform a task in a guaranteed time frame

Question 25

what is the bios

Answer 25

the program a computer’s microprocessor uses to start the computer system after it is powered

Question 26

describe the power on self start routine

Answer 26

• ensures all hardware are correctly connected and functional
• checking cpu clock, memory and processor is operational
• testing for external memory devices connected to the computer

Question 27

what is a bootstrap

Answer 27

the program which loads the operating system from the hard disk to the main memory

Question 28

what are device drivers

Answer 28

programs which allow the os to interact with hardware

Question 29

what is a virtual machine

Answer 29

a theoretical computer that is a software implementation of a computer system

Question 30

what does a virtual machine do

Answer 30

it provides an environment with a translator for intermediate code to run

Question 31

what is intermediate code

Answer 31

code that is halfway between machine and object code

Question 32

whats the advantage of intermediate code

Answer 32

saves money and time of having to purchase multiple devices for testing

Question 33

other uses of virtual machines?

Answer 33

• protection from malware
• running incompatible software