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A level OCR Computer Science > 1.2.1 System software > Flashcards

1.2.1 System software Flashcards

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1
Q

what is the purpose of an operating system?

A

it provides an interface for the user to interact with the hardware

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2
Q

What are the different functions of the operating system?

A
  • providing a platform for application software to run
  • providing a user interface for the user to interact with the computer in a familiar and easy way
  • utility programs to help maintain the computer
  • memory/resource management
  • file management
  • device drivers
  • handles interrupts
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3
Q

what are interrupts?

A

when any device requires the attention of the processor

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4
Q

what is multitasking?

A

when you have more than one program open and running at the same time

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5
Q

how does the computer multitask?

A

the processor allocates small amounts of time for each process and cycles between them

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6
Q

what does the operating system do during multitasking?

A

assigning a time slice to each task, letting it process and then moving onto the next one so quickly it appears to happen at the same time

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7
Q

how is data stored?

A

in files

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8
Q

what are extensions to filenames?

A

an added part to a filename which tells the operating system which application to load the file into

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9
Q

how does the operating system present files?

A

a logical structure of files in folders and allow the user to rename, delete, copy and move files

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10
Q

what is user management?

A

allowing multiple users to log into the same computer

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11
Q

what does the operating system do for user management?

A

retain the settings for each user
recall which access rights different users have
a client-server network may impose a fixed or roaming profile for a user and manage login requests to the network

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12
Q

what is the user interface?

A

the way in which you interact with the computer as a human being

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13
Q

what are the features of WIMP?

A
  • windows, icons, menus, pointers
  • visual
  • intuitive
  • interactive
  • optimised for mouse and touch gesture input
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14
Q

why is it inefficient to move programs already loaded into RAM when there are gaps in between the programs?

A
  • takes a lot of time to move a program as addresses and free space references need to be updated
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15
Q

what are pages?

A

fixed size sections of a program made to fit sections of memory
(thought of as physical divisions)

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16
Q

what is paging?

A

the splitting of a program to fit into a given number of pages

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17
Q

what is the downside of paging?

A

it takes no account of how it splits the program
this means it could split the program inefficiently

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18
Q

what are segments?

A

different sized
complete sections of programs
logical divisions

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19
Q

what is segmentation?

A

splitting a program into logical segments so that it fits in memory

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20
Q

what are some similarities of segmentation and paging?

A
  • both allow programs to run despite insufficient memory
  • pages and segments are stored on disk
  • pages and segments are transferred into memory when needed
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21
Q

what are the differences of paging and segmentation?

A
  • pages are fixed sized. Segments are different sizes
  • Pages are made to fit sections of memory. Segments are complete sections of programs
  • Pages are physical divisions. Segments are logical divisions
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22
Q

what is virtual memory?

A

when programs are swapped/switched between main memory and a space on secondary storage. This allows more programs to appear like they are open.

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23
Q

what is an interrupt?

A

a way to signal to the processor that other applications or devices require attention.

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24
Q

how is the FDE cycle adapted for interrupts?

A
  1. Fetch
  2. Decode
  3. Execute
  4. Check for new interrupts
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25
Q

what is the interrupt service routine?

A

a program with a set of instructions that need to be fetched, decoded and executed to carry out the operations of the interrupt

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26
Q

when an interrupt happens, what needs to change with the registers and addresses in the CPU?

A

the contents of the program counter need to be changed to point to the address for the first instruction of the interrupt

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27
Q

How does the processor know to continue the previously executing program once the interrupt is complete?

A

when an interrupt is received, the values held in the registers are copied into a data structure in memory called the stack

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28
Q

how are the values from the registers added and removed from the stack?

A
  • they are pushed onto the stack in a stack frame - saving them for later retrieval
  • the frame is then popped off the top of the stack
29
Q

what does popping the frame off the stack allow the computer to do in relation to handling interrupts?

A

Allows the computer to:
- retrieve the previous values for the original program
- load them back in to the processor registers
- carry on executing the original program where we left off

30
Q

what happens when an interrupt is interrupted with a higher priority interrrupt?

A
  • the first interrupt service routine is pushed onto the top of the stack along with the original executing program
  • the second interrupt is then executed
  • once the second interrupt is executed, the frame on top of the stack is popped which retrieves the values for the first interrupt
31
Q

what are some example hardware interrupts?

A
  • power supply failure
  • power/reset button pressed
  • power-down command
32
Q

what are some example user interrupts?

A
  • moving the mouse
  • clicking/tapping an icon to open a new program
  • keyboard presses
33
Q

what are some example software interrupts?

A
  • illegal instruction encountered
  • arithmetic overflow
  • new log-on request
34
Q

what are some example timer interrupts?

A
  • data-logging program reading an input sensor every second
  • screen recording application
35
Q

what are some example input/output devices interrupts?

A
  • buffer nearly empty
  • signal the completion of a data transfer to/from a device
  • printer ink supply notification
36
Q

what is scheduling?

A

uses a scheduler to allow a computer to multitask they can run many applications at the same time. the scheduler allocates time to each application being processed in the CPU

37
Q

what is a scheduler?

A

an OS module that manages which process to execute next and how much time it is allowed to execute

38
Q

what is the ready queue?

A

queue which stores the processes to be processed

39
Q

what is a running state?

A

when the currently executing process finishes, is blocked or suspended, the next process in the ready queue start to run in the CPU

40
Q

what can happen once a process in a running state?

A
  • finish executing and leave system
  • get blocked (if requires an input or output command)
  • run out of allotted time so is suspended and moved to the back of ready queue
41
Q

how does first come first serve work?

A
  • processes executed in the order they arrive
  • processes behind each other have to wait until the one in front is done
42
Q

how does shortest job first work?

A
  • picks the processes that take the shortest amount of time and runs them until they finish
  • scheduler needs to know how long processes take
43
Q

how does round robin worK?

A
  • each process is allocated a fixed amount of time (= time slice/quantum)
  • if process is not complete by the end of time slice, returns to queue
44
Q

how does shortest remaining time work?

A
  • job with the shortest remaining time is first
  • when new job arrives, length of time it takes is compared to the remaining time of current job
  • if new job takes less time then current job is suspended and new job run
45
Q

how do multi-level feedback queues work?

A
  • separates processes into multiple ready queues based on processing needs
  • gives preference to processes with short CPU bursts
  • gives preference to processes with high input/output bursts
  • input/output bound processes will sleep in a wait queue to give other processes time
46
Q

what are the advantages of shortest job first?

A

reduces number of waiting jobs and the number of smaller jobs waiting behind larger ones

47
Q

what are the disadvantages of shortest job first?

A

need to know the length of the each job in advance

48
Q

what are the disadvantages of shortest remaining time?

A

same as shortest job first
(need to know length of time for each job in advance)

49
Q

what are multitasking OSs?

A

lets more than one program run at the same time

50
Q

what are multi-user OSs?

A

lets multiple users interact with system
(also lets users interact with system at the same time)

51
Q

what is a distributed OS?

A

combining the processing power of several computers across a network for a single task

52
Q

what does the OS do in distributed computing?

A
  • controls and coordinates computers
  • presents the computers to user as if they were a single computer
53
Q

what are embedded OSs?

A

run on dedicated hardware for max. efficiency using low-powered processors and little memory

54
Q

what are real-time OSs?

A

guarantees to process events or data within a certain amount of time

55
Q

how are real-time OSs built?

A

lots of redundancy to handle abnormal increases in input

56
Q

what is BIOS?

A

responsible for loading the OS when the computer first turns on
- stands for Basic Input/Output System

57
Q

what are the 4 main functions of the BIOS?

A
  • POST
  • Bootstrap (boot) loader
  • BIOS drivers
  • BIOS or CMOS setup
58
Q

what is POST?

A
  • Power On Self Test
    tests computer hardware and ensures no errors exist before loading OS
59
Q

what is bootstrap (boot) loader?

A

locates the OS and loads the OS kernel into memory and BIOS passes control to it

60
Q

what are BIOS drivers?

A

low levels drivers which give the computer basic operational control over hardware

61
Q

what is BIOS or CMOS setup?

A

configuration program used to configure hardware settings (inc. system settings)

62
Q

what is a device driver?

A

a program which tells the OS how to control and communicate with a particular hardware device (usually comes with device)

63
Q

what is the purpose of device drivers?

A
  • operate + control devices attached to computer
  • provide interface between OS and device
  • tells OS how to communicate with device
  • translates requests between device and computer
64
Q

what is a virtual machine?

A

a program that has the same functionality as a physical computer

65
Q

what are some uses for virtual machines?

A
  • emulators to play old games
  • emulators to test software on different platforms
  • test new versions of an OS
66
Q

what are virtual servers used for?

A

increasing the number of servers in a system by having the physical servers run multiple virtual servers

67
Q

what is intermediate code or bytecode?

A

a half-way code that source code is compiled into
it then gets translated by a virtual machine into the specific machine code

68
Q

why is intermediate code (bytecode) used?

A

means code is highly portable between devices
(gives a standardised code)

A level OCR Computer Science (21 decks)

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