1.2.1 Systems Software

Question 1

1.2.1 A)
What is an os

Answer 1

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

Question 2

1.2.1 B)
Why is memory managment needed

Answer 2

memory must be shared fairly between multiple programs as ram not large enough to hold all. so os allocated amount of procosser time each task gets

Question 3

1.2.1 B)
What are the three types of memory managment

Answer 3

paging, segmentation and virtual memory

Question 4

1.2.1 B)
What is paging

Answer 4

memory is split up into equal sized section these can be swapped in and out of memory from secondary storage. However could seperate instructions like a loop.

Question 5

1.2.1 B)
What is segmentation

Answer 5

splits memory into logical size division which may vary in size. Represents the structure and logical flow of program.

Question 6

1.2.1 B)
What is virtual memory

Answer 6

uses a section of seconday storage to act as ram. part of program not in use temp moved through paging.
However disk thrashing can occur, this is when the computer freezes due to pages being swapped to frequently so they are spending move time moving instructions then executing them.

Question 7

1.2.1 C)
What is an interrupt

Answer 7

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

Question 8

1.2.1 C)
How are interrupts stored

Answer 8

based on priority on urgent stored in order of priority within an abstract data structure callled priority qeue which is in the interrupt register

Question 9

1.2.1 C)
How does Interrupt servies routine work

Answer 9

1)At the end of the fde cycle processor checks content of interrupt register
2) if an iterrupt of higher prority is found the content of the memory registers are temp transfered to a stack
3)cpu then responds to interrupt by loading the correct interrupt servies routine into the ram. A flag is sent to signal that the ISR began
4) Queue checked again for interrupts, this is repeated untill all have been servises. All interrupts have higher priorty then regular programs
5) pop the frame of the stack to continue the fde cycle

Question 10

1.2.1 D)
What is scheduling

Answer 10

function of OS to ensure all sections of programs being run (jobs) recieve a fair amount of processing time.
How long , what next ??

Question 11

1.2.1 D)
What catagories can schedulings algorthims be placed into

Answer 11

pre-emptive
non pre-emptive

Question 12

1.2.1 D)
pre-emptive vs non pre-emptive

Answer 12

Pre - jobs are activly made to stop and start by using the os
non pre - once job starts left alone untill completion

Question 13

1.2.1 D)
What are types of pre-emptive scheduling algorthims

Answer 13

Round robin
multi-level feedback
shortest time remaining

Question 14

1.2.1 D)
What are types of non pre-emptive scheduling algorthims

Answer 14

First come first serve
shortest job first

Question 15

1.2.1 D)
explain the round robin scheduling algorthim

Answer 15

Each job given section of processor time (slice) to execute. All jobs have equal time untill complete and removed from queue. Long jobs are ineff , doesnt take prority into account

Question 16

1.2.1 D)
explain the first come first serve scheduling algorthim

Answer 16

Chronological order from joining queue

Question 17

1.2.1 D)
explain the multi-level feedback scheduling algorthim

Answer 17

multiple queues with diffrent priorites , difficult to implicate

Question 18

1.2.1 D)
explain the shortest job first scheduling algorthim

Answer 18

req processer to calc how task takes. risks processor stavation if continuious short jobs join queue

Question 19

1.2.1 D)
explain the shortest time remaining scheduling algorthim

Answer 19

req processer to calc how task takes. risks processor stavation if continuious short jobs join queue but if a shorted job joins queue it will take priorty

Question 20

1.2.1 E)
What are the diffrent types of OS explain

Answer 20

1) distributed - runs across multiple devices allowing the
load to be spread accross multiple computer cpus
2) Embedded - preforms a small range of specific tasks consumes less power
3) multi-tasking - multiple userrs make use of some computer must use scheduling alg risk of cpu starvation
4) real time - used in critcal time computers were takes happen in a guaranteed time frame

Question 21

1.2.1 F)
What is BIOS

Answer 21

Basic input output system, first system to run pc relies on it for running tests before loading OS into memory

Question 22

1.2.1 F)
What are the tests that bios carry out

Answer 22

1) POST - power on self test ensures hardware are correctly connected and functional
2) checks cpu clock , memory and cpu is operational
3) tests for external memory

Question 23

1.2.1 F)
Why is bios needed

Answer 23

As OS can only be loaded into the RAM from secondary storage

Question 24

1.2.1 F)
What is a bootstrap

Answer 24

Loads OS kernel into main memory

Question 25

1.2.1 F)
What is a kernel in terms of BIOS and OS

Answer 25

Kernel ensures smooth OS interface between hardware and software

Question 26

1.2.1 G )
What is a device driver

Answer 26

Program that provided by the OS allowing OS to interact with hardware by translating OS instructions into instructions the hardware will understand
specific to computers architecutre

Question 27

1.2.1 H)
What is a virtual machine

Answer 27

A Virtual Machine (VM) is a computer resource that uses software instead of a physical computer to run programs and deploy apps

Question 28

1.2.1 H)
What are the benifits of a virtual machine in terms of a server

Answer 28

can split a physical server into many so if one fails another can pick it up.

Question 29

1.2.1 H)
What are the properties of a VM
+ve and -ve

Answer 29

Provides an environment with a translator to run intermediate code. +VE )This allows for an evironment for testing different OS saves time and money of purchasing another device with a different OS.
-VE ) can ve slower running intermediate code on a VM compared to low level code.

Question 30

1.2.1 H)
What are some other uses for VM’s

Answer 30

Protection from malware - malware will effect the VM not the physical device its being run on.
Allows user to run incompatable software - able to run os specific programs like a console on a pc

Question 31

1.2.1 H )
What is intermediate code

Answer 31

halfway between machine code and object code