1.2.1 Systems Software

Question 1

OS

Answer 1

refers to collection of programs that work together to provide an interface between user and computer

Question 2

OS Features

Answer 2

• memory management
• resource managment
• file management
• device drivers
• interrupt managment
• utilities
• security
• UI

Question 3

Memory management

Question 4

paging

Answer 4

memory is split up into physical, equal-sized sections known as pages

Question 5

segmentation

Answer 5

splits up memory into logical sized divisions, segments.

Question 6

Virtual memory

Answer 6

used section of hard drive to act as RAM, sections of programs not currently in use temporarily removed into VM, via paging - freeing up space in RAM

Question 7

issue with VM (disk thrashing)

Answer 7

computer freezes, as pages being swapped too frequently between hard disk to main memory

Question 8

interrupts

Answer 8

signals generated by software/hardware to indicate to processor that process needs attention

interrupts stored in order of priority, OS responsible to ensure interrupts serviced fairly by processor.

Question 9

interrupt service routine

Answer 9

processor checks contents of interrupt register at end of each FDE cycle. If interrupt exists of higher priority to current, current contents of registers in cpu temporarily transferred into stack. Processor responds by loading ISR into RAM, flag is set ISR has begun

Question 10

scheduling

Answer 10

ensure all sections of programs being run (jobs) recieve fair amount of processing time

Question 11

pre-emptive

Answer 11

jobs actively made to start/stop by OS

eg. MLFQ, SRT, RR

Question 12

NON PRE-EMPTIVE

Answer 12

once job started, left alone until complete

eg. FCFS, SJF

Question 13

Round robbin

Answer 13

each job given section of processor time (time slice) within its allowed to execute. Once job finished, OS grants another slice, repeats until job is complete.

longer jobs = longer duration time as execution inefficiently split

ignores job priority

Question 14

FCFS

Answer 14

jobs processed in order in which they enter queue

Question 15

MLFQ

Answer 15

makes use of multiple queues, each ordered based on different priority

difficult to implement due to deciding which jobs to prioritise

Question 16

SJF

Answer 16

jobs processed in order according to time required for completion.

Requires processor to know how long each job take

risk of processor starvation, which is when a process is
not given adequate processor time to execute and complete.

Question 17

SRT

Answer 17

processed according to time left for completion, jobswith least time to completion serviced first.

risk of processor starvation, which is when a process is
not given adequate processor time to execute and complete.

Question 18

distributed OS

Answer 18

os runs across multiple devices allowing load to spread across multiple computer processors

Question 18

types of OS

Question 19

embedded OS

Answer 19

built to perform small range of specific tasks

Question 20

multi-tasking OS

Answer 20

enables user to carry out task simultaneously, done by time slicing

Question 21

multi-user OS

Answer 21

MULTIPLE USERS CAN MAKE USE OF ONE COMPUTER, scheduling algorithm used.

risk of processor starvation, which is when a process is
not given adequate processor time to execute and complete.

Question 22

real time OS

Answer 22

designed to perform a task within a guaranteed time frame.

Question 23

BIOS

Answer 23

basic input output system

Question 24

BIOS

Answer 24

program that runs when a computer system is turned on

Question 25

BIOS responsible for running key tests before OS loaded into memory

Answer 25

- POST (power-on self test) >> ensures all hardware is correctly connected - checking CPU clock >> memory/processor is operational - testing for external memory devices connected to computer

Question 26

bootstrap

Answer 26

program that loads the OS from the hard disk into main memory.

Question 27

what is a device driver

Answer 27

a program supplied with a peripheral that allows OS to control and communicate with the device

Question 28

Virtual machines

Answer 28

theoretical computer including a software implementation of a computer system.

Question 29

intermediate code

Answer 29

code halfway between machine code and object code

Question 30

why use Virtual machines?

Answer 30

commonly used to create a development environment for programmers to test programs on different OS. ADV: - saves time/money of having to purchase multiple devices for testing DisAdv: - running intermediate code in Virtual machine can be slower compared to running low-level code on device its designed for

Question 31

other used of virtual machines

Answer 31

- protection from malware >> malware will affect VM rather than device being used - running incompatible software >> programs specific to different OS can be run within a VM (saves time/money)