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AS-Level Compsci > Section 2 Systems Software > Flashcards

Section 2 Systems Software Flashcards

1
Q

Why is an operating system necessary?

A

To manage operations of the computer from the user
Because the user cannot directly communicate with the hardware

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2
Q

Define OS

A

A set of programs that managed the operations of a computer for the user

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3
Q

Where is the OS stored?

A

the hard disk

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4
Q

List the different tasks that OS handle? (6)

A

Peripheral/file management
interrupt handling
security
providing a platform for software to run
providing a user interface
processor scheduling

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5
Q

Why is memory management needed

A

for multitasking on devices
allowing for users to switch between multiple running applications
eg streaming music then editing a document

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6
Q

Why use paging or segmentation?

A

They split memory into small sections for optimum use

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7
Q

What is paging?

A

Memory is divided logically into fixed size pages of 4Kb each
A process in memory may be held in several non-contiguous pages
Logical memory and physical memory locations are linked by a page table which shows both addresses

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8
Q

What is segmentation?

A

Logical division of address space in main memory into varying length segments which depend on the program structure

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9
Q

Why is virtual memory needed?

A

Memory is limited
Many jobs might need to be loaded into memory, so some jobs need to be loaded to secondary storage as an extension of memory to make room for the next job

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10
Q

Benefit and drawbacks of virtual memory

A

more memory can be used than is available in RAM
it may take long if many jobs are in VM as the OS spends most of its time swapping pages in and out of RAM, slowing performance

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11
Q

What is a interrupt? Give an example of each of the 3 types.

A

a signal from a software program, hardware device or internal clock to the CPU
software: application program terminates or requests certain services from the OS
hardware: error in printing such as out of paper
clock: triggered by timer regularly to indicate it’s the next process’s turn

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12
Q

Describe the flow of the Fetch execute cycle with interrupt checking

A

Start
fetch next inst
decode inst
excecute inst
any interrupts to be processed?
if yes, interrupt service routine is tun
if not, continue to next instruction

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13
Q

Examples of 3 interrupts with descrnding priorities

A

power fail interrupt
clock interrupt
an i/o device sending a signal requesting service or end of i/o operation

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14
Q

What is responsible for allocating processor time to each application running simultaneously?

A

the OS

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15
Q

What is multi-tasking in computers?

A

Processors complete small tasks of multiple larger tasks in turn, giving the appearance of them running similtaneously

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16
Q

describe the job of a scheduler?

A

the OS module responsible for ensuring processor time is used as efficiently as possible
this is very complex in large multi user networks eg accessing the same database

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17
Q

Objectives of the scheduler (4)

A

maximise throughput
be fair to all users on a multi user system
provide acceptable response time to all users
ensure hardware resources are kept as busy as possible

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18
Q

state 5 scheduling algorithms

A

round robin
first come first served
shortest remaining time
shortest job first
multi level feedback queues

19
Q

describe round robin

A

processes despatched in first come first serve basis
each process given a limited time slice of cpu time
if the process isn’t complete before it’s time expired/a higher priority interrupt occurs, the despatcher gives the CPU to the next process
uses an interval timer to generate regular scheduled interrupts
guarantees a reasonable response time for all users of the system

20
Q

describe first come first served

A

jobs processed in the order they arrive
no priority system

21
Q

describe SRT scheduling

A

processes with smaller ETC are run next
reduced number of small jobs waiting behind big jobs
however, knowledge of job ETC required

good for batch jobs such as payroll or any scientific jobs run regularly

22
Q

describe SJF scheduling

A

process with the smallest ERT (estimated running time) is run next
same issues as SRT
if a uni student runs a small program, their output will be much faster than large research programs when being run at the same time

23
Q

describe multi level feedback queues

A

designed to
give preference to short jobs and I/O bound processes
separate processes into categories based on their need for the processor

since i/o processes are slower than processor speed, keeping peripherals busy prevents bottlenecks from occuring when several programs need to send data to the printer for example

24
Q

List the 6 types of OS

A

distributed
embedded
multitasking
multiuser
realtime

25
Q

what is a distributed operating system

A

a form or parallel processing
spreads load over multiple computer servers
single job is split up and each subtask is run on a separate computer
eg school intranets

26
Q

what is a multitasking system

A

can be in standalone pcs
appears to run simultaneously by switching rapidly between jobs

27
Q

what is a multiuser (and multitasking) systems

A

a multitasking system but with time sharing systems added so each user’s tasks are carried out by the CPU

28
Q

Smartphone 2 types of OS

A

OS for user interface and running applications
realtime OS

29
Q

what is an embedded OS?

A

found in hardware eg washing machines m/microwave ovens
requirements change to match where it’s to be used

30
Q

what is a real time OS?

A

real time embedded system

it must:
respond very quickly to inputs from sensors
be able to deal with many inputs simultaneously
have failsafe mechanisms to detect and take action if any hardware fails

31
Q

What is the BIOS

A

program stored in EPROM (erasable programmable rom) that starts computers after they are initially turned on
it initialises and tests hardware and loads the OS into RAM from hardware

32
Q

what is a device driver?

A

a program providing a software interface to a particular hardware device
this enables OS to access hardware functions without knowing the details of the hardware used

33
Q

what is a virtual machine?

A

any instance where software is used to take on the function of the machine including executing intermediate code

or running an OS within another to emulate different hardware

34
Q

systems software meaning

A

software needed to run computer hardware and application programs

35
Q

applications software 2 types and difference

A

general purpose - eg word processors can be used for many different processes
special purpose - eg hotel booking systems

36
Q

types of utility programs

A

disk defrag
auto backup
auto update
virus checking
compression softwarr

37
Q

off the shelf vs bespoke software

A

OTS less expensive, B more costly due to expertise
OTS may contain unwanted features and not have some good features, B is cutomised to user requirements
OTS is ready for installation instantly, B may take a long time to develop
OTS is well documented, well tested and error free, B may contain errors that do not surface immediately

38
Q

open source vs freeware vs closed source

A

OS licensed for anyone to use
OS must be distributed with source code for modification
OS devs can sell software they created
modified OS software programs have to be open source too

freeware is free for use with restrictions and no access to source code

CS is sold in the form of a licence to use it
CS will have restrictions eg 50 users on one site (site licence)
CS may have regular updates and a support team

39
Q

Choosing an application thought process

A

does it provide all necessary functionality?
does it run on the available hardware?
is it available off the shelf or is it specially written?
cost??
is it well used, tried and tested?

40
Q

What is an assembler

A

Converts assembly code programs to machine code

41
Q

what is assembly code?

A

low level language
each inst is one machine code inst
dependent on hardware

42
Q

what is a compiler? how does it work?

A

a program translating high level languages eg python to machine code

object code can be saved and run without compiler use again

43
Q

what is an interpreter?

A

translates line by line from HL code into machine code after checking for syntax errors
needs to be run every time

44
Q

Compiler vs interpreter advantages of each

A

c:
object code can be saved on disk and run whenever needed
object code executes faster than interpreted code
object code can be distributed without a compiler present
object code is more secure

i:
source code can run on any machine with an appropriate interpreter available
useful for program dev as there’s no need for lengthy recompilation when errors are found

AS-Level Compsci (10 decks)

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