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comsci - structures and functions of the processor > functions of OS > Flashcards

functions of OS Flashcards

1
Q

operating system

A

manages the hardware and provides an interface for the user and application software

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2
Q

boot loader

A

stored in ROM, loads the OS into RAM when t he computer is turned on

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3
Q

OS functions

A

user interface, memory management, interrupt handling, processor scheduling

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4
Q

memory management

A

the allocation and management of memory between programs in use

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5
Q

paging

A

memory is divided into fixed sized pages, process may be held in several non-contiguous ones

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6
Q

page table

A

maps between the physical and logical memory locations

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7
Q

segmentation

A

the logical division of memory into varying length segments

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8
Q

virtual memory

A

an area of the hard disk designated to supplement RAM

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9
Q

interrupt

A

signal sent from hardware, software or clock to alert the CPU that it needs instruction

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10
Q

software interrupt

A

occurs when an application program terminates or requests a certain service from the OS

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11
Q

hardware interrupt

A

occurs when an I/O operation completes, error occurs (ie printer out of paper)

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12
Q

dealing with interrupts

A

when an interrupt signal is received, execution of the running program/process is suspended and all lower priority interrupts are disabled, the values in the registered are then put onto the system stack and the ISR routine handles the interrupt, once it’s been serviced the original values of the registers are retrieved from the stack and the original process resumes

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13
Q

low priority interrupt - examples

A

an I/O device sends a signal requesting service or signalling end of I/O

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14
Q

medium priority interrupt - examples

A

clock interrupt

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15
Q

high priority interrupt - examples

A

power-fail interrupt

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16
Q

multi-tasking

A

carrying out small parts of multiple larger tasks in turn giving the appearing of carrying out several tasks simultaneously

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17
Q

scheduler

A

the operating system module responsible for making sure that processor time is used as efficiently as possible

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18
Q

scheduler - objectives

A

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

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19
Q

round robin

A

each process is given an equal time slice, if it doesn’t finish within it’s slice it joins the end of the queue

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20
Q

first come first served

A

processes are dealt with in the order they arrive

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21
Q

shortest remaining time

A

picks the process with the shortest estimated time remaining time to finish, the scheduler will switch to a new process with a shorter

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22
Q

shortest job first

A

picks the process with the shortest estimated running time and runs it until it finishes

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23
Q

multi-level feedback queues

A

multiple queues with different priorities are used

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24
Q

disk thrashing

A

excessive swapping of pages between RAM and virtual memory which noticeably slow down the computer

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25
Q

round robin - advantages

A

guarantees a reasonable time for all processes to be executedin

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26
Q

round robin - disadvantages

A

doesn’t consider priority

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27
Q

first come first served - advantages

A

simple/easy to implement

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28
Q

first come first served - disadvantages

A

doesn’t consider priority

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29
Q

shortest remaining time - advantages

A

higher throughput

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30
Q

shortest remaining time - disadvantages

A

starvation, user has to estimate the job time

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31
Q

shortest job first - advantages

A

higher throughput

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32
Q

shortest job first - disadvantages

A

starvation

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33
Q

multi-level feedback queues

A

uses multiple queues with different priority levels giving preference to short jobs and I/O bound processes

34
Q

distributed OS

A

a parallel processing system which distributes work load over multiple computers

35
Q

multi-tasking OS

A

a single processor can appear to do multiple tasks simultaneously by scheduling processor time

36
Q

multi-user, multi-tasking systems

A

a single mainframe is connected to dozens/hundreds of terminals all using the mainframe CPU, each gets a slice of processor time according to a scheduling algorithm

37
Q

mobile OS

A

the main OS manages the UI and application software, a low-level proprietary real-time OS which operates the radio and other hardware

38
Q

embedded OS

A

has minimal features and UI, accept sensor input and output to control devices, applications stored in ROM, limited RAM

39
Q

real-time OS

A

must respond very quickly to inputs or sensors, must be able to deal with many simultaneous inputs, must have failsafe mechanisms and hardware redundancy

40
Q

basic input output system (bios)

A

stored in EPROM, initialises and tests the system hardware and loads the OS Into RAM

41
Q

device driver

A

hardware dependent and OS specific computer program that provides an interface to a particular hardware enabling the OS to access hardware functions

42
Q

virtual machines

A

software used to emulate a machine (used for running one OS on another or executing intermediate code)

43
Q

systems software

A

software needed to run the computer’s hardware and application programs

44
Q

utility programs

A

software designed to optimise the performance of the computer

45
Q

disk defragmentater

A

a program that reorganises a magnetic hard disk so files which have been split are recombined making reading faster

46
Q

defragmentation - SSD

A

data is accessed randomly thus fragmentation doesn’t affect access speed additionally this shortens the lifetime

47
Q

automatic backup

A

users may forget to backup files, this can be automated by specifying the destination (where), the sources (what) whether it’s compressed (how), and when

48
Q

automatic updates

A

detects software update releases and automatically installs them

49
Q

virus checker

A

scans permanent storage for viruses by comparing files to known virus definitions, sometimes uses heuristics (looks for types of behaviour likely to be used by a virus) to guess which programs are viruses

50
Q

compression software

A

reduces the size of files so they can be transmitted or stored

51
Q

application software

A

software that performs a task to benefit the user

52
Q

general-purpose software

A

word-processor, spreadsheet, graphics package

53
Q

special-purpose software

A

payroll and accounts packages, hotel booking systems, fingerprint scanning systems

54
Q

off the shelf software

A

ready made software available to anyone to purchase

55
Q

bespoke software

A

software that is custom created for a specific user

56
Q

off the shelf - properties

A

less expensive due to wider customer base, may contain unwanted features, ready to be installed immediately, well documented, well tested, error free

57
Q

bespoke software - properties

A

more costly, customised features, potentially long development time, may contain errors which don’t surface immediately

58
Q

open source software

A

allows anyone to access its source code, licensed but free to use, anyone may modify the software and sell it if the software is also open source

59
Q

closed source/proprietary software

A

does not allow access to source code, users must pay copyright owner for a licence, potentially restrictions on how the software can be used

60
Q

freeware

A

software is free but source code isn’t available

61
Q

selecting an applciation

A

functionality, hardware compatibility, availability, cost, reliability

62
Q

assembly code

A

a low level language where each instruction is a TLA and almost always equivalent to one machine code instruction

63
Q

assembler

A

translates assembly code to machine code

64
Q

compiler

A

translates a high level language to machine code in one go

65
Q

interpreter

A

translate and execute code line-by-line stopping if the line contains an error

66
Q

compiled langages

A

C++ visual basic

67
Q

interpreted languages

A

python, javascript

68
Q

bytecode

A

source code (java) is compiled into bytecode, an intermediate step between source code and machine code, which is then converted by an interpreter

69
Q

compilers advantages

A

produce an executable file (no need to recompile), hide source code from end user

70
Q

compilers disadvantages

A

must be reinterpreted if code is changed, can only be executed on a certain device

71
Q

interpreters - advantages

A

can be run on any machine with the appropriate interpreter, useful for program development (no need to recompile everytime error occurs)

72
Q

interpreters - disadvantages

A

slower to run

73
Q

stages of compilation

A

lexical analysis, syntax analysis, code generation, code optimsation

74
Q

lexical analysis

A

white spaces and comments are removed, compiler will create tokens of keywords, constants and identifiers and keywords are assembled into a symbol table

75
Q

symbol table

A

entries in the table show the identifier/keyword, the kind of item, the data type of the item, the run-time address/value

76
Q

syntax and semantic analysis

A

tokenized code i s compared to the syntax rules and errors are generated if rules are broken, checks for semantic errors

77
Q

code generation

A

object code is generated

78
Q

code optimsiation

A

code is optimised for efficiency, aims to remove redundant instructions and replace inefficient code

79
Q

libraries

A

pre-written, compiled and tested programs that offer shortcuts

80
Q

linkers

A

put the appropriate machine addresses in all the external call and return instructions so modules are linked correctly

81
Q

libraries - advantages

A

they are tested and error-free, save time

82
Q

loaders

A

copies the program and any linked subroutines into main memory to run

comsci - structures and functions of the processor (9 decks)

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