1.2.1

Question 1

OS

Answer 1

operating system

Question 2

the need for an OS

Answer 2

allows the user to interact with hardware using a user interface

Question 3

the function of an OS

Answer 3

Device driver
User
Application software
Memory/resource management
User interface
Hardware
Utility programs
File management
Interrupt handling

Question 4

Multitasking

Answer 4

When you have more than one program open and running at the same time.
rge processor flits between them all so quickly it seems like it is happening at the same time

Question 5

file management

Answer 5

allows you to: copy, delete, move files

Question 6

user management

Answer 6

Allows multiple users to log into the same computer
each user can have different access levels

Question 7

memory management

Answer 7

moving the location of a program in memory so the free space is together.
it is not desirable in practice.
takes a lot of time to move a program in memory or on disk, as addresses and free space references all need updating

Question 8

paging

Answer 8

Pages are fixed size physical divisions.
Programs are split up to fit into a given number of pages.
Paging takes no account of how it splits the program, only that it splits it into fixed-sized pages.
It could separate the instructions inside a looping condition so they are in different pages, (isn’t efficient).

Question 9

segmentation

Answer 9

Segments are different sized logical divisions.
Based on logical divisions, segmentation splits the program into multiple parts and places them in the available free space, leaving smaller areas of free space.

Question 10

virtual memory

Answer 10

when there are too many open files and the computer can not keep all of them open at once because there is not enough space in RAM.
The least recently used file is put into secondary storage temporarily. If the user keeps trying to use all the files then they will have to keep swapping from the current memory to secondary storage which may cause disc thrashing.

Question 11

interupts

Answer 11

when a program or other device needs immediate attention and needs to signal to the processor
(Interrupts always have a higher priority than normal programs)

Question 12

the role of interupts and ISRs

Answer 12

interrupt service routine is simply a program with a set of instructions that need to be FDEed to carry out the operations of the interrupt
the contents of the program counter need to be changed to point to the address for the first instruction of the interrupt
the values held in the registers are copied into a data structure in memory known as the stack

Question 13

interupts and ISRs within the FDE cycle

Answer 13

Fetch
Decode
Execute
Check for new interrupts

Question 14

round robin sheduling

Answer 14

ecah process is allocated a fixed amount of run time (time slice)
executes a FCFS but if the process is not finished in the time slice it is moved to the back of the queue

Question 15

first come first serve sheduling

Answer 15

the processes are executed in the order they arrive

Question 16

multi-level feedback queues sheduling

Answer 16

Several ready queues are used, each with a different scheduling algorithm.
Jobs can move between queues as their priorities change.

only if a computer system has more than one processor or processor core

Question 17

shortest job first sheduling

Answer 17

needs to know how long each process takes (orders the current list)

the shortest run time is executed first

Question 18

shortest remaining time sheduling

Answer 18

similar to SJF but its pre-emptive

if a new item is added that is shorter it will be moved to the front of the queue

Question 19

distributed OSs

Answer 19

the operating system controls and coordinates many computers, presenting them to the user like a single system

Question 20

embedded OSs

Answer 20

tend to run on dedicated hardware so they run with maximum efficiency, using low-powered processors and very little memory.

Question 21

multi-tasking OSs

Answer 21

multiple process seemingly taking place at the same time

Question 22

multi-user OSs

Answer 22

multiple users using a system

Question 23

real time OSs

Answer 23

processes have to execute within a known time frame

lots of redundancy is built into these systems so they can handle sudden increases in input

(rarely run at ful capacity)

redundancy - backup components/systems to ensure uninteruptted running

Question 24

BIOS

Answer 24

Basic Input Output System
responsible for loading the operating system when the computer first turns on

Question 25

bootstrap

Answer 25

A boot loader program is used to load the operating system kernel into memory

Question 26

device drivers

Answer 26

Software that tells the operating system how to communicate with a device

Question 27

virtual machines

Answer 27

trick a program into thinking it’s running on its native hardware when, in fact, it’s running on an entirely different machine

Question 28

virtual machines - executing immediate code

Answer 28

java code is an example of intermediate code running on a virtual machine (designed to run on many different platforms)

it compilies its code into a half-way code known as bytecode or intermediate code

the code is translated by a Java Virtual Machine running on a target device, which then translates it into specific machine code

Question 29

virtual machines - running an OS within another

Answer 29

you can run nearly any OS of your choosing in a virtual machine