CompSci - Operating Systems

Question 1

OS Types

Answer 1

Batch
Single-User
Multi-User
Multi-Tasking
Multi-Programming

Question 2

OS Types - Batch

Answer 2

Executes several tasks simultaneously without user interaction

Used for data processing like billing

Question 3

OS Types - Single-User

Answer 3

Operated by one user at a time

The user interacts with a personal computer.

Question 4

OS Types - Multi-User

Answer 4

Operated by several users at a time

Used for DBMSs and cloud platforms

Question 5

OS Types - Multi-Tasking

Answer 5

Can quickly switch between processing several tasks, giving the illusion of parallelism

Used for personal computing

Question 6

OS Types - Multi-Programming

Answer 6

Allows to load several programs into memory at once, optimising CPU utilisation during it.

Used for personal computing.

Question 7

Causes of Interrupts

Answer 7

Hardware interrupts
Software interrupts
Timer interrupts
User interrupts

Question 8

Software Interrupts

Answer 8

Triggered by important software instructions or errors

Question 9

Hardware Interrupts

Answer 9

Triggered by I/O signals or component failure

Question 10

Timer Interrupts

Answer 10

Triggered at regular intervals for multitasking

Question 11

User Interrupts

Answer 11

User input

Question 12

Interrupts

Answer 12

Signals that signify that immediate attention is required for something. Anything being currently processed is temporarily paused.

Question 13

Interrupt Handling

Answer 13

OS suspends the current interrupt handling routine
Current CPU state is saved in memory
OS initiates the higher priority interrupt handling routine
Once it’s finished, the OS reloads the CPU state and it resumes its previous function.

Question 14

Interrupt Priorities

Answer 14

Since multiple interrupts can occur at once, the OS needs to be able to decide which to deal with first.

High / Imminent component failure
Medium / Timer interrupt
Low / I/O signals

Question 15

Factors In Allocating Priorities To Interrupts

Answer 15

Urgency
Stability Significance
Frequency of Occurence
Resource Dependence

Question 16

Purpose of Memory Partitioning

Answer 16

Dividing RAM into blocks of memory so that several programs can be loaded and run simultaneously.

Multi-programming support
Efficient memory use
Isolation

Question 17

Consequences of Memory Partitioning

Answer 17

pretty much the same as fixed and variable fields

Fixed Partitioning:
Redundant space
Easy to process

Variable Partitioning:
Complex to process
No redundant space

Question 18

Methods of Data Transfer

Answer 18

CPU is responsible for moving data, constantly checks if the device is ready
The device sends interrupts as “handshakes” to signify that data was sent
A dedicated controller moves the data

Question 19

Buffers

Answer 19

Temporary memory areas to hold data in peripheral devices while it is being transferred between devices to account for difference in speed of the devices.

Single Buffering / One memory area is used
Double Buffering / Two memory areas are used, so that one can be filled while the other emptied.

Double buffers increases active time of the device, optimise CPU usage and lower time delay for interrupt handling.

Question 20

Resource Priority Management

Answer 20

Processor allocation - Manages which tasks can be processed in a queue
Hardware allocation - Manages access to hardware resources like memory

Prevents overload
Maintains system responsiveness
Balances tasks for maximum optimisation

Question 21

States of A Process

Answer 21

Running - Being executed
Ready - Waiting for CPU allocation
Blocked - Waiting for an event to occur

Question 22

CPU Process Management

Answer 22

Time-Slicing - CPU time is divided into units that is distributed among processes
Polling - CPU costantly checks a device to see if it’s ready
Threading - CPU processes several tasks within one process, paralellism