YEAR 1 CO1 WEEK 24 OS (MEMORY MANAGMENT) AND WEEK 25 (TYPES OF OS, SCHEDULING)

Question 1

What is an operating system?

Answer 1

Core software controls how a computer operates.

Question 2

What are the purpose of operating systems?

Answer 2

• Provides a user interface
• Managing hardware/peripherals
• Memory management
• Manages CPU/handles interrupts
• Provides security
• Provides a platform to run other systems/software
• Provides utilities for system maintenance

Question 3

What are the parts of the operating system?

Answer 3

• The Kernel (heart of operating system)
• Device drivers
• The user interface
• System utilities

Question 4

What is the kernel?

Answer 4

Kernal in different operating systems may be responsible for slightly different blend of tasks.

Loading/unloading applications from memory.
Memory management.
File management.
Data security.

Question 5

How does the kernel work?

Answer 5

Designed for operating system

Question 6

What is a File Allocation Table (FAT) and what does it do?

Answer 6

A map of where your files are stored on a hard disk

• Stores pointers/addresses to the start of files
• Stores file names, file sizes and access rights
• It allows the OS to identify free space in memory

Question 7

What is NTFS (New Technology File System)

Answer 7

New Tech File System which supports larger hard drives, file sizes and longer file names

Question 8

What is a device driver ?

Answer 8

It’s a script / info that enables the operating system to control and interface with hardware

Question 9

What is GUI

Answer 9

Graphical user interface is a friendly way for people to interact with computers

Question 10

What is CLI

Answer 10

Command line interface
Simpler cause it’s text base

Question 11

What are the types of scheduling

Answer 11

Round robin
First come first serve
Shortest job first
Shortest remaining time
Multi level feedback queue

Question 12

What is round robin?

Answer 12

Gives an equal amount of time being processed
Probs it a time slot so if to much it get ignored until comes back round, don’t do priority
Advantages simple to implement

Question 13

What is First come first serve

Answer 13

What ever one comes first is dealt with first
Disadvantage
Other jobs have to wait for the first to be done
No priority system

Question 14

What is Short job first

Answer 14

Does the smallest first
Minimise the advantages
Long task could get left for ages

Question 15

What is multilevel feedback queue

Answer 15

Takes Ito account priority and Priority’s can be adjusted
Very complicated
Not very efficient if jobs all same priority

Question 16

What is Shortest remaining time

Answer 16

Quickest job left to complete finish first

Question 17

Define A Logical Address

Answer 17

Addresses at which an item appears to reside, generated by CPU.

Question 18

Define Physical Addresses

Answer 18

Actual physical location of the storage cell in memory.

Question 19

What needs to happen for a executable application to be run.

Answer 19

To run a process it has to be loaded into main memory.
To run more than one process all have to be in main memory at the same time.
When executable application loaded into main memory it becomes a ‘process’ and requires memory to run.

Question 20

Describe Segmentation.

Answer 20

OS sets aside memory for process to use. This is called segmentation.
A way of portioning memory.
Variable Sized based on contents.
Are logical divisions which hold complete sections of programs.

Question 21

Define Paging.

Answer 21

Second type of memory management which designed to handle virtual memory.

Question 22

Define a Page.

Answer 22

A fixed sized physical division of memory. Each page is contiguous.

Question 23

Describe Pagination.

Answer 23

When RAM full memory manager determines least used page.
Page then copied into virtual memory.
Free area renumbered by memory manager and marked as free to use.
If page needed again swapped back into RAM.
ONLY USED WHEN VIRTUAL MEMORY IN USE.

Question 24

What is Disk Thrashing.

Answer 24

When Virtual Memory in heavy use.
As more pages are swapped eventually more time is being spent swapping pages than processing data.c

Question 25

Describe the MutiTasking OS.

Answer 25

allows more than one program to run at the same time (appear to).
Arranges for every process to have some CPU time, switching between processes.

Question 26

Describe the MultiUser OS.

Answer 26

Allows multiple users, on different workstations, to access a single powerful computer via a network.
Handles the needs of users by dividing up CPU time and assigning blocks to each user in time.

Question 27

Describe what happens in turn for a multiuser OS.

Answer 27

Each user logs onto system + presented with their workspace.
Allocates resources for jobs they want to run.
Keeps log of how much processing time and resources they use.
Works out most efficient use of computer processing cycles.
Maintains security + privacy between the different users.

Question 28

Describe the Distributed OS.

Answer 28

Controls a number of computers at the same time to undertake a single computer intensive task.
Each computer contains part of the overall OS.

Question 29

Describe the Real Time OS.

Answer 29

Designed to handle input data within a guaranteed response time (latency).
Specifically designed to be extremely reliable and to have precise and consistent timings.

Question 30

Describe the Embedded OS.

Answer 30

Computer hardware designed to handle a specific task on a specific system hardware.
Hardware resources usually limited due to size of object or functions it is required to perform.

Question 31

Describe the Batch OS.

Answer 31

Common on a mainframe computer specifically with massive repetitive data processing in mind.
Requires separate programs for input, process and output.

Question 32

What is the OS of a multitasking computer expected to do and how is it made possible?

Answer 32

The OS of a multitasking computer is expected to run many programs in memory without any noticeable delay.
Made possible by scheduling which is the task of allocating CPU processing time amongst all running programs.

Question 33

Describe Round Robin scheduling algorithm.

Answer 33

Each process given equal amount of time being processed.
Queue made holding all processes that are ready to be run. Each loaded into main memory in turn.
Each process given set amount of time to use.
If completed within time next process loaded immediately otherwise put back in queue to wait for another turn.

Question 34

State advantages and disadvantages of Round Robin.

Answer 34

Advantages:
Easy to implement
Disadvantages:
Not take account of priority.
Not take account that some processes much longer than others.

Question 35

Describe First Come First Server scheduling algorithm.

Answer 35

Lines up all processes ready to run in First In First Out queue.
Allows processes to run to completion.

Question 36

State advantages and disadvantages of First Come First Serve.

Answer 36

Advantages:
Simple algorithm to implement.
Disadvantages:
Not take into account of priority.
Not consider some processes longer than others.
Once job started prevents other jobs from being processed until its complete.

Question 37

Describe Shortest Job First Scheduling Algorithm.

Answer 37

Processes arranged in queue by how much time (FDE cycles) each process needs to run to completion.
If newer process comes along scheduler will work out processing time and slot in appropriate point in queue.
If shorter than current process running program interrupted and shorter one runs immediately.

Question 38

State advantages and disadvantages of Shortest Job First Algorithm.

Answer 38

Advantages:
Ensures short jobs aren’t kept waiting for long processes.
Minimises average time process takes to complete.
Disadvantages:
Not take into account priority.
Longer jobs that are nearly done still interrupted by shorter jobs.

Question 39

Describe Shortest Time Remaining Scheduling Algorithm.

Answer 39

For Shortest Job algorithm 1000 cycle job still be interrupted by 700 cycle as total length shorter than old one.

Fixed by ordering jobs by how much time they have remaining.
Jobs only interrupted if new process shorter than time remaining before completion.

Question 40

State advantages and disadvantages of Shortest Time Remaining Algorithm.

Answer 40

Advantages:
Allows short processes to be handled very quickly.
Disadvantages:
Not take into priority.
Long jobs may never be completed if short jobs keep jumping the queue.

Question 41

Describe Multi-Level Feedback Queues Scheduling Algorithms.

Answer 41

Maintains a number of queues with different priority levels.
Each job given priority by scheduler and then sorted into relevant queue.
High priority queue completed first then each of the lower queues in turn.

Question 42

State advantages and disadvantages of Multi-Level Feedback Queues.

Answer 42

Advantages:
Takes in account of priority.
Disadvantages:
Complex to implement.
Low priority may take extremely long time to complete.