Operation Systems

Question 1

Operating systems (meaning and how it manages things)

Answer 1

> 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.

Question 2

Boot Loader (what it does)

Answer 2

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

Question 3

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

Answer 3

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

Question 4

The 4 main parts of the OS:

Answer 4

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

Question 5

KERNEL (Task which it does)

Question 6

KERNEL (Task which it does)

Answer 6

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

Question 7

Device driver (Task which it does)

Answer 7

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

Question 8

User Interface (Task which it does)

Answer 8

> It allows a person to interact with the computer.

Question 9

3 Different types of User Interface

Answer 9

> 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

Question 10

System Utilities(Task which it does)

Answer 10

> Performs background task such as file management

Question 11

Memory management

Answer 11

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

Question 12

Memory segmentation / Segmentaion

Answer 12

> ## 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.

Question 13

segment/section (size)

Answer 13

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

Question 14

paging/ pagination(meaning and how it works)

Answer 14

> 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

Question 15

process

Answer 15

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

Question 16

Virtual memory (meaning and how it works )

Answer 16

> 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

Question 17

Disk Thrashing

Answer 17

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

Question 18

Scheduling(and scheduler)

Answer 18

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

Question 19

Scheduler ensures that the computer:

Answer 19

> 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

Question 20

First come Firs served (meaning)

Answer 20

> The first job to arrive is executed until completion

Question 21

First come First served ( Pros and cons)

Answer 21

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

Question 22

Shortest Job First ( meaning)

Answer 22

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

Question 23

Shortest Job First (pros and cons)

Answer 23

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

Question 24

Shortest remaining time (meaning)

Answer 24

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

Question 25

Shortest remaining time (pros and cons )

Answer 25

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

Question 26

Round Robin ( meaning)

Answer 26

> 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

Question 27

Round Robin (pros and cons)

Answer 27

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

Question 28

Multiple level feedback queues( meaning)

Answer 28

>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

Question 29

Multiple level feedback queue ( pro and cons )

Answer 29

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

Question 30

Polling (meaning)

Answer 30

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

Question 31

polling (pros and cons)

Answer 31

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

Question 32

Interrupt (meaning)

Answer 32

> 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

Question 33

Interrupt can be sent to CPU by :

Answer 33

> software > hardware devices > CPU's internal clock

Question 34

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

Answer 34

> 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

Question 35

Interrupt priority

Answer 35

> 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

Question 36

examples of interrupts:

Answer 36

> 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

Question 37

Timer Interrupt

Answer 37

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

Question 38

Restart Interrupt

Answer 38

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

Question 39

Program error Interrupt

Answer 39

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

Question 40

hardware error interrupt

Answer 40

> 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

Question 41

I/O interrupt

Answer 41

> every time you press our mouse

Question 42

Priority list

Answer 42

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

Question 43

CPU's three choices of what it does with interrupts

Answer 43

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

Question 44

latancy

Answer 44

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

Question 45

stack overflow

Answer 45

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