Topic 2.6 - The Operating System

Question 1

What is the definition of an Operating System?

Answer 1

It is software which manages the operation of the computer by controlling hardware and application software.

Question 2

Name five resources which the operating system manages?

Answer 2

It manages all hardware and software including:

• Memory
• The processor
• Peripherals
• Backing store
• The interface

Question 3

How does the operating system manage memory?

Answer 3

• It ensures all programs and data (including itself) is stored in correct memory locations
• Ensures that programs and data cannot corrupt one another
• Manages cache memory via the cache controller
• Can allocate part of secondary storage to be used as virtual memory if the RAM fills up

Question 4

How does the OS manage the processor?

Answer 4

• On a multi-tasking OS, it makes it appear that processes are running simultaneously by allocating time slices
• Ensures that different processes don’t interfere with each other

Question 5

How does the OS manage peripherals?

Answer 5

• Manages peripherals such as input and output devices
• Communicates with the device drivers either sending an output or receiving an input (give examples)
• Allows communication with peripherals at very high speeds even when the CPU is dealing with other processes

Question 6

How does the OS use spooling?

Answer 6

Spooling is similar to a buffer however uses disk space to queue jobs for a device until it’s ready to accept them

• Spooling needed as peripherals and processors run at different speeds
• Jobs received in correct order when device is free
• Useful in batch processing (e.g. payroll payslip printing)
• Useful as user can carry on working / log off whilst waiting for job to print for example

Question 7

What is polling?

Answer 7

This is where the operating system periodically and sequentially sends signals to devices to check their status. Used to ensure each process gets its appropriate share of processor time.

Question 8

How does the OS manage the backing store?

Answer 8

• Ensures that data is stored and can be retrieved correctly from any disc drive
• Creates and maintains a filing system such as FAT or NTFS
• Organise files in a hierarchical directory structure

Question 9

What are the different attributes a file can have?

Answer 9

• Read-only
• Write
• Amend
• Delete
• Archive
• System
• Hidden

Question 10

How does the OS manage user accounts?

Answer 10

• Allows creation and deletion of user accounts
• User profiles make it possible to allocate access rights to a group of users in one go
• Maintain user profiles with appropriate restrictions (e.g. Admin, Staff, Student)

Question 11

How does the OS provide an interface for the user?

Answer 11

• Provides useful icons (e.g. recycle bin)
• Provides menus / drop-down lists for easy choices
• Allows the creation and use of hot keys
• Allows the creation, deletion, copying, moving, sorting and searching of files and folders
• Allows easy navigation of files and folders
• Allows customisation of desktop
• Allows user to have multiple windows open
• Allows users to switch between windows
• Allows user to copy data across applications
• Provides user with error / warning / help messages

Question 12

what is the purpose of utility software?

Answer 12

They are designed to help analyse, configure, optimise and maintain the computer.

Question 13

Name 5 different forms of utility software:

Answer 13

• Anti-virus
• Firewall
• Defragmentation
• Cookie removal
• File manager
• Task manager

Question 14

What are the three different modes of operation?

Answer 14

• Batch Processing
• Real-Time Control
• Real-Time Transaction

Question 15

Describe batch processing:

Answer 15

• All inputs and data is collected first
• Once the efficient batch process has begun, there is no more intervention by the user
• Batches usually processed at night when the system is relatively underused
• Batch processing can be used when individual users submit jobs which are then processed as a batch

Question 16

Describe real-time control:

Answer 16

• These systems are automatic and require no user interaction
• Often sensors are used to constantly monitor conditions
• Inputs are processed immediately
• Outputs are adjusted immediately
• e.g. ABS or air conditioning units

Question 17

Describe real-time transaction:

Answer 17

• When a user views a record, they are locked out
• The record is updated immediately
• This ensures that no two users can book the same ticket
• e.g. plane tickets or concert tickets

Question 18

What are the four different types of system?

Answer 18

• Single User
• Multi-programming
• Multi-user
• Multi-tasking

Question 19

What are the features of a single user system?

Answer 19

• Windows allow multiple users access to a PC, but only one at a time
• It is a standalone system
• The computer is not connected to a network
• Unable to communicate with other computers or share data or devices
• Protected from viruses/hackers
• Not susceptible to network failure

Question 20

What are the features of a multi-programming system?

Answer 20

• Two or more programs are held in main memory at the same time
• The programs appear to be running simultaneously
• Uses partitioning
• Uses scheduling
• Means processor time isn’t being wasted

Question 21

What is scheduling?

Answer 21

The real-time clock causes regular interrupts to create time-slices which the OS allocates to the various jobs.

Question 22

What is partitioning?

Answer 22

This is the allocation of a portion of memory to a process and ensuring those portions don’t overlap and corrupt one another.

Question 23

What is threading?

Answer 23

This is where a process is split up into multiple mini-processes known as threads which can be used to perform background tasks.
- Uses modern computers multiple cores

Question 24

What are the features of a multi-tasking system?

Answer 24

This is a multi-programming system applied to a single user machine.

Question 25

What are interrupts?

Answer 25

Interrupts are signals sent by the various hardware devices and internal units to tell the processor that they need attention. Each type of interrupt is associated with an interrupt handler.

Question 26

What is the purpose of an interrupt handler?

Answer 26

An interrupt handler is a software procedure that takes control when the interrupt occurs to deal with the event/error.

Question 27

What happens when a device sends an interrupt?

Answer 27

• The processor checks and detects the interrupt register for different types of interrupts
• The program currently being executed is halted
• An interrupt service routine is executed
• The original program continues from where it left off

Question 28

What needs to be considered when there a multiple interrupts occurring at the same time?

Answer 28

• The priorities of the interrupt need to be checked
• A high-level interrupt may interrupt the servicing of a lower level interrupt
• Interrupts with high priority include impeding data loss, impending hardware/software failure and the detection of imminent power failure.

Question 29

What are program control blocks used for?

Answer 29

These are used to store the state of the currently executing program whilst an interrupt is being dealt with.

Question 30

What is buffering?

Answer 30

Uses memory to control data coming into / out of peripherals as they run at different speeds. Buffers are used in two processes, firstly the buffers need to be filled with data and secondly for the buffers to transfer the data to be processed.

Question 31

Why is double buffering preferred over single buffering?

Answer 31

Double buffering is preferred as when one buffer is being filled, the other buffer can be transferring the data which is more efficient.

Question 32

What are the three different process states?

Answer 32

• Ready (waiting for a time slice)
• Running (being executed)
• Blocked (error received, e.g. needs data from input)