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Computer Science > Operation Systems > Flashcards

Operation Systems Flashcards

1
Q

Operating systems (meaning and how it manages things)

A

> The operating system is the core software that controls how a computer operates.(eg, windows or IOs)
It manages the hardware and provides an inter face for the user and the application software.

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2
Q

Boot Loader (what it does)

A

> The boot loader in ROM loads the OS into RAM when the computer is switched on

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3
Q

Functions the OS provides: (there’s 6 of them)

A 
> User Interface
> Memory Management
> interrupt handling
> Processor scheduling
> Device management
> Handles security
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4
Q

The 4 main parts of the OS:

A

> the Kernel
the Device drivers
the user interface
the system utilities

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5
Q

KERNEL (Task which it does)

A
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6
Q

KERNEL (Task which it does)

A

> loading/unloading application from memory
scheduling tasks to run more efficiently on the CPU
memory management
data security

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7
Q

Device driver (Task which it does)

A

> A device driver enables the OS to control and communicate with the device
(eg.)
> Internal: Graphics card, hard disk
> External: Printer, Mouse

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8
Q

User Interface (Task which it does)

A

> It allows a person to interact with the computer.

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9
Q

3 Different types of User Interface

A

> Graphical - which makes use of picture, graphics and icons
Command line - which allows the user to directly interact with the computer system by typing in commands
Natural Language - Interacting with the computer directly using your voice

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10
Q

System Utilities(Task which it does)

A

> Performs background task such as file management

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11
Q

Memory management

A

> Memory management is done when the program and/or data is loaded into the RAM.
OS manages the allocation RAM for programs

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12
Q

Memory segmentation / Segmentaion

A

> ## memory segmentation is the allocation of segments or sections of memory to allow a process to runSegmentation is when the OS sets aside memory for a process to use.

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13
Q

segment/section (size)

A

> Aren’t fixed size and will be as large as needed.

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14
Q

paging/ pagination(meaning and how it works)

A

> This is where available memory is divided into equal sized chunks called pages (each page has a memory address)

> A process will be then loaded into the main memory but they may not be contagious(close together in physical terms)

> Memory manager gives each page a number and records it in a page table

> only used if virtual memory is in use

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15
Q

process

A

> when an executable application is loaded in the main memory it becomes a process

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16
Q

Virtual memory (meaning and how it works )

A

> Virtual memory is an area in the hard disk designated as temporary storage
Some pages of a current process are stored in VM until they are needed to be swapped back into the RAM

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17
Q

Disk Thrashing

A

> Repeatedly swapping pages in and out VM can noticeably slow don the computer .

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18
Q

Scheduling(and scheduler)

A

> The task of allocating CPU processor time amongst all running programs.
The software inside of the OS that manages scheduling is a Scheduler

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19
Q

Scheduler ensures that the computer:

A

> Maximises the use of CPU time
Prioritise jobs
Alter priority
Ensures no task is uncompleted for too long, even if it is low priority
Tries to minimalize the delay between user request and it’s completion time

20
Q

First come Firs served (meaning)

A

> The first job to arrive is executed until completion

21
Q

First come First served ( Pros and cons)

A

Advantage:
> simple to implement
> once a process start it keeps going until completion

Disadvantages:
>Once a jobs starts it will not stop
>Does not take priority into account
>Does not consider the length of processes

22
Q

Shortest Job First ( meaning)

A

> The shortest job is executed to completion unless a shorter jobs arrives, then it will take over the current process

23
Q

Shortest Job First (pros and cons)

A

Advantages:
>Maximises num of shortest jobs completed
>minimises average time for processes to complete

Disadvantages:
> Shorter jobs keep jumping queue
> Does not take priority into account

24
Q

Shortest remaining time (meaning)

A

> The shortest remaining time is executed until completion unless a job with a shorter remaining time comes and takes over the current process

25
Q

Shortest remaining time (pros and cons )

A

Advantages:
>short processes are handled very quickly
> Maximum num of processes completed in a given time

Disadvantages:
>Longer jobs may not be completed as shorter jobs keep jumping through
>Does not take priority into account

26
Q

Round Robin ( meaning)

A

> Jobs are allocated a time slice (by FIFO) during when they can use the CPU’s resources.
If the job isn’t finished another get allocated a time slice

27
Q

Round Robin (pros and cons)

A 
Advantages:
> simple to implement
> good overall if priority is similar
Disadvantages:
> Does not take priority into account 
> does into consider length into account
28
Q

Multiple level feedback queues( meaning)

A

> Multiple queues with different levels of priority
If a process uses to much of the CPU’s time it gets moved to a lover priority queue
can also be moved up the queue id waited long

29
Q

Multiple level feedback queue ( pro and cons )

A

Advantages:
>ensures higher priority jobs run on time
> makes sophisticated use of process priority

Disadvantages
>complex to interrupt
> not efficient if all jobs may take extremely long if high priority jobs arrive

30
Q

Polling (meaning)

A

> Polling is the regular checking of an event to see whether it has happened

31
Q

polling (pros and cons)

A

Advantages:
> simple, predictable as polling only occurs at specific points while the software runs

disadvantages:
> may be inefficient in terms of using up CPU’s processing time

32
Q

Interrupt (meaning)

A

> are signals generated by a hardware device or by a software application, seeking the attention of the CPU, once interrupt is competed the CPU can go back to what it is doing.
external events usually get generated by external devices

33
Q

Interrupt can be sent to CPU by :

A

> software
hardware devices
CPU’s internal clock

34
Q

How is an interrupt detected during the fetch-execute cycle? and what happens after?

A

> It checks the Interrupt register (which stores interrupts) when each cycle is completed

> When and interrupt is detected the processor stops fetching instructions and instead pushes the current contents of it’s registers onto a stack

> It then uses the Interrupt Service Routine to deal with the service

35
Q

Interrupt priority

A

> interrupt have different priorities and will be processed in order of priority

> If a higher priority interrupt occurs when an interrupt is being processed, the lower priority interrupt will be put at the top of a stack

36
Q

examples of interrupts:

A

> hardware: power supply failure / power button pressed
user: moving the mouse or pressing a key on the keyboard
software: new log-on request / Illegal instruction occurred
Timer: screen recording application
Input/output devices: printer ink supply notification

37
Q

Timer Interrupt

A

> This occurs at a fixed time intervals. there are circuit int the computer that can generate an interrupt signal every 1ms

38
Q

Restart Interrupt

A

When you press the reset button on your computer it sends a singanl

39
Q

Program error Interrupt

A

> when a program has an error it will send a signal

40
Q

hardware error interrupt

A

> when some electrical or mechanical faults appear ,then the malfunction device send an interrupt signal to CPU
to at least output the message on the VDU

41
Q

I/O interrupt

A

> every time you press our mouse

42
Q

Priority list

A

1 ) hardware failure

2) reset interrupt
3) program error
4) timer interrupt
5) I/O interrupt

43
Q

CPU’s three choices of what it does with interrupts

A

1) stop what it’s doing to start service to the interrupt
2) carry on what it is doing until it’s completed, then start service on the current interrupt
3) carry on what it is doing until it’s completed, then start service on the previous interrupt going in ascending order

44
Q

latancy

A

. the delay between an input into the system and the desired output as the result

45
Q

stack overflow

A

> is an undesirable condition in which a particular computer program tries to use more memory space than the last call stack has available

Computer Science (3 decks)

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