Operating System Flashcards

1
Q

Operating system

A

a program or set of programs that manage the operations of the computer for the user. It acts as a bridge between the user and the computer’s hardware, since a user can’t communicate directly with hardware. It disguises the complexities of managing and communicating with hardware from the user via a simple interface where they can click and immediately achieve tasks

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2
Q

where is OS held

A

permanent storage e.g. hard disk

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3
Q

the loader*

A

a small program held in ROM. When computer is turned on, the loader in ROM sends instructions to load the OS by copying it from storage to RAM

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4
Q

functions of OS

A

all OS share basic functions:

  • processor scheduling
  • UI
  • provide utility software to carry out household tasks
  • memory management and file handling
  • ISR
  • backing store management
  • management of all I/O
  • security for user files
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5
Q

how memory management works

A

each program/open file/copied clipboard item must be allocated a SPECIFIC area of memory whilst computer is running. When switching applications, both in memory simultaneously. If program closed, relinquishes memory and then free space. you don’t need to load the whole program into memory initally

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6
Q

paging

A

partitioning memory: memory divided into fixed page sizes eg 4kB and are physical divisions. a process held in memory may be held in several non-contigous pages. consecutive logical memory addresses physically stored in separate pages anywhere within physical memory and age table uses mapping to store link between physical memory address and virtual memory address.
used for virtual memory

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7
Q

page table does what

A

uses mapping to store the link between physical and logical memory address, preventing running out of memory and putting two things in the same place

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8
Q

why segmentation and paging

A

shuffling things in memory takes time so split up and makes better use of memory
both use VM and allow programs bigger than memory to run and allow non contiguous torage

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9
Q

segmentation

A

a way of partitioning memory by the logical division of memory into varying length segments of complete sections of programs depending on structure of program

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10
Q

virtual memory

A

Allows programs to run when insufficient memory available
as more jobs are loaded into memory OS may store PAGES (fixed sizes) of temoporarily inactive jobs onto disk as memory isn’t limitless. acts as secondary backing storage, an extension of memory to make room for pages next job with share of PROCESSOR TIME

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11
Q

large number of jobs loaded leads to

A

deterioration of performance as insuff. memory in RAM, pages swapped in and out until more time spent swapping than processing instructions- slows down PC (thrashing)

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12
Q

interrupts

A

a signal from a software program, hardware device or internal clock to the CPU as a request for processing time when requiring immediate attention, causing a break in the execution of the current routine. It allows important tasks to take precedence/be processed. Also allows multitasking

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13
Q

software interrupt

A

when an application program terminates or requests certain services from OS e.g. I/O operation complete, or error occurred e.g. printer out of paper

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14
Q

timer interrupt

A

indicates its time for next process to have processor time

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15
Q

memory management and why its necessary

A

To do with the organisation of main memory via converting logical addresses to physical addresses. OS manages allocation and management of space. Partitioning is used, involving paging/segmentation and virtual memory.

  • allows memory to be Managed more easily
  • allows Optimum use of memory
  • allows programs to Share/be allocated memory and protects programs/data from each other
  • allows you to work on Several at a time.
  • allows running when Insufficient space in memory/allows running programs larger than main memory
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16
Q

first come first serve is inefficient

A

once a job starts- prevents other jobs being processed.

a job using slow resource e.g. printer wastes processor time

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17
Q

when a CPU receives an interrupt signal

A

It suspends execution of running program/process and lower priority interrupts. It puts values of program counter and each register and PC onto the system stack. Meanwhile source of interrupt is identified and ISR called to deal with interrupt- a particular routine will be run to service it depending on type of interrupt. after interrupt serviced original values of registers retrieved, interrupts are enabled and process resumes from point left off from

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18
Q

hardware interrupt eg

A

hard disk READ SET OF DATA BLOCKS

buffer is full or has free space

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19
Q

interrupts are assigned…

A

priorities (order of importance) and lower priorities may be disabled whilst a higher priority is being serviced, allows processes to take place and precedence

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20
Q

order of priority

A

power fail, clock, IO device sends signal requesting service or signalling end of IO operation

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21
Q

when are interrupt tests done

A

at end of each FDE cycle

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22
Q

processor scheduling

A

OS allocates processor time for each application as they compete for CPU because computers are able to run multiple applications simultaneously

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23
Q

a single processor can…

A

only process one instruction at a time but can multitask thanks to interrupts

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24
Q

single user multitasking

A

can run on a STANDALONE computer. only one user uses machine AT A TIME. constantly switching between small parts of multiple larger tasks in turn, according to SCHEDULING ALGORITHMS allowing more than one task (apparently) to be carried out at a time. giving appearance of carrying out several tasks simultaneously. Several tasks are in memory at one time but most not currently being executed

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25
what is the scheduler*
the OS module responsible for ensuring processor time is used as efficiently as possible, allocating processor time to applications competing for CPU acc to scheduling algorithms
26
objectives of scheduler
- allow the processing, prioritisation of tasks and multitasking - be fair to all jobs - able to prioritise jobs and ensure they get processed (no starvation) - maximum throughput (process as many jobs possible in least possible time) - be fair to all users - ACCEPTABLE RESPONSE TIME to all users (main aim)- maximise number of interactive users with fast/real time response time - make max/efficient use of CPU time and other resources - keep hardware as busy as possible
27
round robin*
>>PREEMPTIVE <>FIFO<< basis , and each have a limited/quantum very small time slice of CPU time, managed by interrupting timer generating interrupts. If process not completed/higher priority occurs dispatcher gives CPU to next user/job and puts VALUES onto system STACK. Job put at back of queue. Some systems have a system of priorities so higher priority has more than 1 consecutive time slice (order may depend on users priorities) Users are unaware of any delays
28
adv and disadv round robin
starvation free, all get a time slice v takes longer for all jobs not always able to PRIORITISE
29
first come first served
jobs processed in order of arriving with NO SYSTEM OF PRIORITIES
30
disadv first come first served
if one large job comes all little ones have to wait a long time
31
shortest remaining time
a preemptive algorithm meaning process will be blocked by scheduler after a fixed time. Smallest estimated time to completion is run next
32
adv shortest remaining time and shortest job first
greater throughput/yield, less WAITING time, less smaller jobs BEHIND BIG JOBS, smaller jobs done quicker and advantages to new jobs
33
disadv of shortest remaining time and shortest job first
requires knowledge of how long a job will take so user has to estimate job time large jobs may never get time share if smaller jobs keep coming (process starvation) or high priority interrupts
34
good jobs for shortest remaining time
batch jobs (group of records processed as a single unit without user inputs) eg payroll done regularly and overnight, scientific and commercial jobs run regularly
35
shortest job first
non-preemptive, won't be blocked by scheduler after a fixed time. Shortest estimated time run next
36
multi-level feedback queue*
several job queues are implemented which jobs can move between: depending on how much processor time they use, characteristics of CPU bursts and need for CPU. Give PREFERENCE to short jobs, IO bound processess
37
multilevel feedback queue: IO devices
IO devices are much slower than CPU so keep as busy as possible to prevent BOTTLENECK because SEVERAL PROGRAMS NEED to send data to same IO device. When 1 job using IO, another uses processor TO MAXIMISE PROCESSOR USE
38
how multilevel feedback queue works
algorithm chooses to process highest priority from corresponding queue and runs. If too much time, moves to lower priority and if waiting too long, moves higher queue
39
adv multilevel feedback queue*
SHORT CPU jobs prioritized and processed quickly, IO bound processes given preference. maximises CPU use, no starvation, preemptive and non preemptive
40
disadv multilevel feedback queue
requires MONITORING and COSTLY
41
backing store management*
OS needs to keep directory of where files are stored and which areas of storage are free so files can be accessed quickly and knows where files and applications can be stored. When files/applic are loaded- transferred FROM backing storage into memory. uses a file management system
42
file management system
COMES WITH desktop OS enabling users to move/delete and protect files and folders from unauthorised access. disguises complexities of managing backing storage
43
what is backing storage
name of all other storage devices aka secondary storage which is non-volatile that is used to store data for a long time
44
main memory
for storing data temporarily which is volatile and stores data and programs whilst in use and being PROCESSED by CPU
45
peripheral management*
different APPLICATIONS require different I/O devices throughout operation. OS communicates with IO to ensure switched on, online, correct device and send correct data
46
when data is sent to IO device
transferred to buffer (area of memory temporarily holding data, that compensates for the difference in speed between IO device and processor) so CPU can continue with another task ALLOWING MAX USE OF CPU
47
interrupts in peripheral management
to know when buffer is filled/emptied so it is requesting for more data to be transferred or to stop sending data
48
distributed OS*
a form of parallel processing that splits and spreads the workload/processing load over multiple, independently networked, physically separate computer nodes/servers/ PROCESSORS. Tasks are run SIMULTANEOUSLY and results are then gathered together, so it APPEARS to be a single system to the user
49
distributed OS is controlled by
a system management software that brings all INTERCONNECTED systems together and coordinates individual and collaborative activity on the different nodes
50
intranets
system configured as a cluster of servers that share MEMORY AND TASKS, providing more POWER than a single large server = better PERFORMANCE
51
mainframe
computers with lots of processors and huge storage simultaneously serving thousands of users (expensive)
52
supercomputers
mainframe designed to go fast than store a lot eg gaming
53
disadv parallel processing
it has to be determined what can actually be split
54
multiuser OS
a single powerful mainframe/supercomputer connected to dozens or hundreds of terminals all using mainframe CPU simultaneously, sharing resources. Each user gets a slice of processor time according to an ALGORITHM
55
multiuser OS manages
each user logged onto system and workspace allocates resources to jobs wanting to run keeps logs of resources and processing time jobs use working out most efficient use of processor CYCLES maintaining SECURITY
56
mobile phone is a
multitasking computer with its own OS
57
mobile phone OS
a OS used on phones/tablets/PDAs and other mobile devices usually TIED TO SPECIFIC HARDWARE combining features of a PC OS with own special features useful for mobile use eg cellular. Made of main system and low level propriety real time OS
58
mobile phone OS special features
responding to users touch, speech recognition, camera, GPS, music player
59
main system mobile OS
operates UI and application software
60
real time mobile OS
radio and other hardware but range of security vulnerabilities permitting others to gain control over mobile device
61
embedded OS
have a dedicated function and usually part of a larger device. Interfaced in a more bespoke manner. Low POWER consumption/COST and use limited HARDWARE and RESOURCES
62
eg embedded OS
washing machine, microwave oven (app program in ROM) control system of passenger aircraft
63
embedded OS interface in household appliance
minimal UI accepts inputs from sensors and sends outputs to control devices no or little RAM and no memory management system no permanent data storage to be managed
64
why are priorities necessary for interrupts
order of importance- to ensure most EFFICIENT use of processor to ensure most urgent task performed first to allow tasks to take place and precedence to choose which interrupt to process if more than one occur together to decide between interrupt and task
65
priorities can change because
allows it to be processed otherwise if higher priorities keep occurring, it would wait indefinitely
66
transfer of memory between main memory and hard disk drive
buffer filled from primary memory and processor can continue with other tasks. Buffer emptied to hard drive. Interrupt sent to processor to request buffer refilled. Interrupt priority determines position in interrupt queue. Process continues until all data transferred.
67
network OS facilities
file handling and save in a remote location communications between machines sharing resources eg hardware, software
68
real time OS
OS running under pre-defined deadlines, completing tasks in a guaranteed time. for tasks classed as time critical where right answer too late is wrong
69
eg RT OS
aircrafts
70
RT OS features
- able to respond quickly to inputs and sensors - must be able to deal with many inputs simultaneously - must have a failsafe mechanism to detect and take appropriate action if hardware component fails - must incorporate redundancy: if a component fails: automatically switches to backup hardware
71
BIOS
basic input output system: firmware designed to run when PC is first switched on. Its responsible for detecting, initializing and testing hardware components and booting OS. historically provided ABSTRACTION layer allowing a consistent way for application programs and OS to interact with IO devices
72
how does BIOS boot OS
copies (key parts) of OS from hard disk to RAM
73
where is BIOS stored
EPROM- erasable programable ROM
74
device drivers*
a computer program providing a software interface to a particular hardware device enabling OS to access hardware functions without needing to know details of the hardware HARDWARE DEPENDENT AND OS SPECIFIC
75
device drivers installation and communication
they may have to be isntalled but OS often comes with common drivers. they are HARDWARE DEPENDENT AND OS SPECIFIC and communicate with devices via system bus/communications subsytem
76
how device drivers work
calling program invokes a routine in the driver, driver issues command to device, device sends data back to driver, driver potentially invokes routines in original calling program
77
virtual machine
any instance where software is used to take on the function of a machine including executing intermediate code or running an OS within another
78
VM user experience
UE is the same on a VM as a dedicated machine. but first choose OS to use
79
benefits of VM
saves costs as reduces need for separate hardware and provides more SECURITY when executing intermediate code
80
virtual device drivers
fools OS into thinking its directly communicating with a certain piece of hardware when actually going through function calls to host