SLR4 - Operating System/Systems Software

Question 1

Explain paging

Answer 1

A method of manipulating memory which uses pages to store code in fixed size blocks and allows programs to run despite insufficient memory. uses virtual memory.

Question 2

Explain segmentation

Answer 2

A method of manipulating memory which uses segments to store code in different sized, logical sections. Uses virtual memory.

Question 3

Define and explain ISR

Answer 3

Interrupt service routine

Determines what happens when an interrupt is raised.

Question 4

Define an interrupt

Answer 4

A signal which stops the fetch, decode, execute cycle from running normally in order to prioritise a different device.

Question 5

Give some examples of interrupts

Answer 5

Hardware:
Power pressed
Memory parity error
Software:
Illegal instruction
Arithmetic overflow
New log-on request
Input/output:
Buffer almost empty
Data transfer completion

Question 6

Define a virtual machine

Answer 6

When software is used to take on the function of a physical machine.
Emulators provide the illusion that a program is running on native hardware.

Question 7

Define and explain OS

Answer 7

Operating system

Software that manages the hardware, software, security and user interface of a computer.

Question 8

Explain the role of the OS

Answer 8

Manages the interrupts in the processor.
Manages memory including paging, segmentation and virtual memory
Manages external devices: OS instructions are converted into instructions that the hardware can read by device drivers.
Manages networking: communication to other devices through protocol
Manages access requests.

Question 9

Define scheduling

Answer 9

A way of managing the amount of time programs have in the CPU.

Question 10

Define memory management

Answer 10

A way of ensuring that programs in memory only access their own data or any authorised shared data with other programs.

Question 11

Define virtual memory

Answer 11

A method of freeing available memory in the RAM by moving unused program sections to the hard drive.

Question 12

Define device drivers

Answer 12

Software which tells the OS how to communicate with a device.

Question 13

Define BIOS

Answer 13

Basic Input Output System
Checks that the computer is functional and loads the OSs kernel into memory
The bootstrap is responsible for loading the OS into memory
Initial start up instructions are stored in ROM
BIOS settings are stored in non-volatile flash memory.

Question 14

Define Intermediate code

Answer 14

Code between source code and machine code which can be read by virtual machines.

Question 15

What are the 5 scheduling algorithms

Answer 15

FCFS - First Come First Served
SJF - Shortest Job First
RR - Round Robin
SRT - Shortest Remaining Time
MLFQ - Multi-level Feedback Queues

Question 16

Explain FCFS

Answer 16

Tasks are executed to completion and in order regardless of time

Question 17

Explain SJF

Answer 17

The shortest task is executed first to completion. The algorithm needs to know the time each job will take in advance.

Question 18

Explain RR

Answer 18

Each task is given a certain amount of time. If it hasn’t finished it re-joins the end of the queue.

Question 19

Explain SRT

Answer 19

The shortest task is executed to completion or until a task with a shorter remaining time joins the queue

Question 20

Explain MLFQ

Answer 20

Multiple queues are used with different priorities and jobs are moved between the queues depending on their behaviour.

Question 21

Define Distributed OS

Answer 21

Controls computers on a network and presents them to the user as one system.

Question 22

Define Embedded OS

Answer 22

Specifically designed for a device and runs efficiently with little memory and low power CPUs

Question 23

Define Multi-tasking OS

Answer 23

Allows multiple application to be open at once by switching between running programs.

Question 24

Define Multi-user OS

Answer 24

Allows multiple users to access a computer simultaneously with individual preferences.

Question 25

Define Real-time OS

Answer 25

Processes are always executed in a certain time frame to cater for unusually high demand, e.g. plane autopilot.