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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
round robin - advantages
guarantees a reasonable time for all processes to be executedin
26
round robin - disadvantages
doesn't consider priority
27
first come first served - advantages
simple/easy to implement
28
first come first served - disadvantages
doesn't consider priority
29
shortest remaining time - advantages
higher throughput
30
shortest remaining time - disadvantages
starvation, user has to estimate the job time
31
shortest job first - advantages
higher throughput
32
shortest job first - disadvantages
starvation
33
multi-level feedback queues
uses multiple queues with different priority levels giving preference to short jobs and I/O bound processes
34
distributed OS
a parallel processing system which distributes work load over multiple computers
35
multi-tasking OS
a single processor can appear to do multiple tasks simultaneously by scheduling processor time
36
multi-user, multi-tasking systems
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
mobile OS
the main OS manages the UI and application software, a low-level proprietary real-time OS which operates the radio and other hardware
38
embedded OS
has minimal features and UI, accept sensor input and output to control devices, applications stored in ROM, limited RAM
39
real-time OS
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
basic input output system (bios)
stored in EPROM, initialises and tests the system hardware and loads the OS Into RAM
41
device driver
hardware dependent and OS specific computer program that provides an interface to a particular hardware enabling the OS to access hardware functions
42
virtual machines
software used to emulate a machine (used for running one OS on another or executing intermediate code)
43
systems software
software needed to run the computer's hardware and application programs
44
utility programs
software designed to optimise the performance of the computer
45
disk defragmentater
a program that reorganises a magnetic hard disk so files which have been split are recombined making reading faster
46
defragmentation - SSD
data is accessed randomly thus fragmentation doesn't affect access speed additionally this shortens the lifetime
47
automatic backup
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
automatic updates
detects software update releases and automatically installs them
49
virus checker
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
compression software
reduces the size of files so they can be transmitted or stored
51
application software
software that performs a task to benefit the user
52
general-purpose software
word-processor, spreadsheet, graphics package
53
special-purpose software
payroll and accounts packages, hotel booking systems, fingerprint scanning systems
54
off the shelf software
ready made software available to anyone to purchase
55
bespoke software
software that is custom created for a specific user
56
off the shelf - properties
less expensive due to wider customer base, may contain unwanted features, ready to be installed immediately, well documented, well tested, error free
57
bespoke software - properties
more costly, customised features, potentially long development time, may contain errors which don't surface immediately
58
open source software
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
closed source/proprietary software
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
freeware
software is free but source code isn't available
61
selecting an applciation
functionality, hardware compatibility, availability, cost, reliability
62
assembly code
a low level language where each instruction is a TLA and almost always equivalent to one machine code instruction
63
assembler
translates assembly code to machine code
64
compiler
translates a high level language to machine code in one go
65
interpreter
translate and execute code line-by-line stopping if the line contains an error
66
compiled langages
C++ visual basic
67
interpreted languages
python, javascript
68
bytecode
source code (java) is compiled into bytecode, an intermediate step between source code and machine code, which is then converted by an interpreter
69
compilers advantages
produce an executable file (no need to recompile), hide source code from end user
70
compilers disadvantages
must be reinterpreted if code is changed, can only be executed on a certain device
71
interpreters - advantages
can be run on any machine with the appropriate interpreter, useful for program development (no need to recompile everytime error occurs)
72
interpreters - disadvantages
slower to run
73
stages of compilation
lexical analysis, syntax analysis, code generation, code optimsation
74
lexical analysis
white spaces and comments are removed, compiler will create tokens of keywords, constants and identifiers and keywords are assembled into a symbol table
75
symbol table
entries in the table show the identifier/keyword, the kind of item, the data type of the item, the run-time address/value
76
syntax and semantic analysis
tokenized code i s compared to the syntax rules and errors are generated if rules are broken, checks for semantic errors
77
code generation
object code is generated
78
code optimsiation
code is optimised for efficiency, aims to remove redundant instructions and replace inefficient code
79
libraries
pre-written, compiled and tested programs that offer shortcuts
80
linkers
put the appropriate machine addresses in all the external call and return instructions so modules are linked correctly
81
libraries - advantages
they are tested and error-free, save time
82
loaders
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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