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Eduqas a-level computer science > the operating system > Flashcards

the operating system Flashcards

paper 2

1
Q

what is an operating system?

A

software that manages and controls the computer hardware + acts as an interface between user and the hardware
eg windows, macOS

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2
Q

OS services (name 3)

A
  • provides user interface
  • runs software programs by loading code + data into RAM and activating CPU
  • allows multiple programs active at same time by sharing processor time
  • allows configuration of hardware eg screen resolution
  • displays catalogue of programs and data files
  • provides security to prevent unauthorised access
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3
Q

how does the OS manage peripherals?

A

manages peripherals (inputs/outputs) by communicating and sending data output to them using drivers

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4
Q

how does the OS manage memory?

A

OS loads data into RAM when needed and unloads it when it isn’t
partitioning
buffering

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5
Q

partitioning

A

dividing memory into multiple partitions and allocating each partition to instructions and data for one specific task

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6
Q

buffering

A

allocating part of memory to temporarily store data in transit between computer and a slower device eg webcam/printer
cannot be filled and emptied at same time so double buffer can be used so one can be filled while the other is emptied to speed up data transfer.

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7
Q

how does the OS manage the backing store?

A

allocate physical disk space as files are added, edited or deleted providing hierarchical, searchable structure for users.

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8
Q

utility software

A

software that performs tasks that support the operating system
analyses processes, optimises processes or maintains the system

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9
Q

categories of utility software (name 4)

A

anti-virus
compression
debuggers
screensavers
system monitors
encryption
defragmentation

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10
Q

anti-virus

A

checks the computer for malware and notifies the user of any is found

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11
Q

compression

A

allows a file/folder to be reduced in size for storage or transmission

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12
Q

debuggers

A

identify and help to resolve problems in software

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13
Q

screensavers

A

starts automatically after a pre-set interval to prevent screen burn and save power

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14
Q

system monitors

A

utilities allow the user to track memory and processor usage + network connection speed and more

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15
Q

name 3 uses of a user interface

A
  • allows copying/ deleting/ moving/ sorting/ searching of file or folders
  • allows access to system settings such as hardware
  • allows users to have more than one window open
  • provides graphical user interface
  • provides user with error messages
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16
Q

modes of operation

A

different ways that operating systems have of working
batch processing
real time control processing
real time transaction processing

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17
Q

batch processing

A

a series of tasks completed at the same time (normally without intervention overnight when resources are available)
uses a transaction file to record events and updates the master file at the end of the period
eg running pay roll, gas billing ( as bills are issued regularly in response to meter readings)
simpler/faster with transactions being stored in order they are recieved

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18
Q

real time control processing

A

reacts to a signal to make changes which will take place immediately (but doesn’t need to happen quickly)
eg traffic lights changing or autopilot detecting obstacle and moving

19
Q

real time transaction processing

A

task completed immediately and the master file is updated when an occurrence is completed to give and accurate view of data at any time
much more complex algorithms
eg used to avoid double bookings at concerts

20
Q

master file

A

holds descriptive data (the actual data that is supposed to be processed) and holds the resultant data after the process is completed
data is held sequentially in key field order
eg customer details for electricity company

21
Q

transaction file

A

contains the transactions (changes supposed to be made to master file)
data is help serially in order it was collected
eg customer meter readings for electricity company

22
Q

singer user OS

A

single user can be active at any one time (can have multiple users but one one at a time)
protected with user names and passwords
home directories are created for each user with a hierarchical file structure
can also be a multi tasking OS

23
Q

multi user OS

A

system resources timeshared between multiple users at once - each can access their own terminals with usernames and passwords
often used on servers
can also be a multi tasking OS

24
Q

multi tasking OS

A

switching tasks in and out of the CPU done by the OS to give the impression it is running everything simultaneously
can falter if one process takes a lot of processing time or crashes as other processes may delay or become unresponsive

25
Q

multi programming OS

A

allows multiple processes to reside in main memory at the same time to make them appear to be processed by the computer’s CPU simulaneously
optimises use of CPU by preventing it from being idle while waiting for slower peripherals. OS may perform scheduling

26
Q

scheduling

A

a processor appears to carry out multiple processes at a time whereas it is actually just switching between them extremely quickly.
scheduler ensures CPU is utilised as much as possible
has different methods of scheduling:
- first come first served
- round robin
- fixed priority

27
Q

first come first served scheduling

A

each process handled from start to finish in the order in which is arose

28
Q

round robin scheduling

A

each process received a fixed time slice and when time slice expired the CPU moves on to next process and come back to incomplete one later

29
Q

fixed priority scheduling

A

high priority processes jump the queue and are handled first. low priority processes can have status upgraded if they are left waiting for a long time

30
Q

time slice

A

a small chunk of processor time

31
Q

states of a process

A

ready - in main memory awaiting execution by CPU
running - currently being executed by CPU
blocked - awaiting access to a resource that is currently unavailable (needs intervention)

32
Q

polling

A

sending a signal to a device eg printer, to check if it is ready.
will repeat until device is ready or computer has polled a predetermined number of times

33
Q

interrupt

A

a signal generated by hardware or software that puts the normal FDE cycle on hold and diverts CPU’s attention to source of the interrupt
has priority levels so another interrupt of higher priority can interrupt an interrupt
a low level interrupt will not interrupt a high level task

34
Q

examples of hardware interrupts

A

mouse click
keyboard press
insertion of new piece of hardware

35
Q

examples of a software interrupt

A

detection of imminent power loss
a runtime error eg attempt to divide by 0
software fault

36
Q

fixed partitioning

A

dividing memory into non-overlapping sections that are fixed in size
process may be loaded into a partition of equal or greater size and is confined to that partition
internal fragmentation can occur

37
Q

internal fragmentation

A

when a small process leaves unoccupied space in a partition

38
Q

variable partitioning

A

system for dividing memory into non-overlapping sections with variable sizes
is more flexible than fixed and doesn’t allow for internal fragmentation

39
Q

dynamic partitioning

A

system for making partitions during run-time according to process’ needs instead of doing it during system configuration
efficiently utilises RAM

40
Q

memory buffering

A

small block of memory in devices where current data is being held and is used to compensate for slower devices
ensures work is not lost when the processor is busy
eg key press on keyboard may be held in buffer if text doesn’t appear when you are typing

41
Q

buffer process for storing and loading data from a device

A

chunk of data sent by CPU to device and stored in a buffer
device will slowly save the data while CPU free do to other tasks
when buffer is empty an interrupt is sent to CPU
CPU processes interrupt by informing OS
then more data is sent and cycle repeats

42
Q

double buffering

A

one buffer used to store the data
the second buffer will process the data
once the data is processed, data from buffer 1 sent to 2 and process repeated
avoids delays and increases processing speed

43
Q

ping pong (method of double buffering)

A

buffer 1 holds data
buffer 2 interrupts and sends the data
buffer 1 interrupts and sends its own data while buffer 2 holds next set of data

44
Q

threading

A

a thread is a sequence of instructions that make up part of a process.
2 threads belonging to the same process can share resources.

Eduqas a-level computer science (12 decks)

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