System software- S2

Question 1

Operation system (OS)

Answer 1

a program or set of programs that manages the operations of the computer for the user.

Question 2

RAM

Answer 2

An internal memory: Random access memory. It’s used to store programs and data that are currently being used. Its is volatile (contents are lost when computer is switched off)

Question 3

ROM

Answer 3

An internal memory: read-only memory. Holds information that needs to be permanently in memory.

Question 4

Give functions of the operation system

Answer 4

Memory management, Interrupts, Processor scheduling,

Question 5

What is the purpose of memory management

Answer 5

• converting logical addresses to physical addresses
• Puts programs into free memory and manages them, making sure they don’t overwrite
• Using paging or segmentation techniques.
• Allows for multitasking.
• Allows for programs larger than the main memory to run (using virtual memory).

Question 6

Whats paging system?

Answer 6

Pages are fixed sizes that are physical divisions and is used in virtual memory but can be used in any memory.
Memory does not have to be held in continuous pages

Question 7

Segmentation

Answer 7

A way of partitioning memory, segments are not fixed size but vary in size, and are logical divisions which hold complete sections of programs.

Question 8

Purpose of virtual memory

Answer 8

A feature of an operating system that allows programs to run when there is insufficient memory available.

Question 9

How is virtual memory done?

Answer 9

temporarily transferring pages of data from RAM to disk storage to make space in memory for the pages needed.

Question 10

What problems can occur with virtual memory

Answer 10

More time spent transferring pages than processing leads to disk threshing and the computer may ‘hang’ (computer program or system stops responding to input).

Question 11

What is an interrupt

Answer 11

Signal sent to the processor requesting for processing time, and for the current execution to be stopped in order to do a more important task.

Question 12

Give example of interrupts

Answer 12

• User interrupt
• Power (failure) = high priority
• I/O interrupt (mouse and keyboard, printer) = low priority
• Clock interrupt (data-logging application that has to read an input sensor every 1 second.) = medium priority
• Software interrupt (software has detected that an error has occurred)

Question 13

Why do interrupts have priorities

Answer 13

Interrupts have priorities to decide between interrupt & current task, or for ensuring when you have more than one interrupt the most urgent task is performed first.

Question 14

What happens when there is an interrupt

Answer 14

• CPU receives an interrupt signal and suspends execution of the current program/process running.
• It disables interrupts of low priority.
• It puts the program counter onto the system stack
• Interrupt Service Routine is called to deal with the interrupt. There are different responses for different interrupts
• Original values of the registers are retrieved from the stack and the process resumes from the point that it left off.
• A test for the presence of interrupts is carried out at the end of each fetch-decode-execute cycle.

Question 15

Processor scheduling

Answer 15

is the operating system module responsible for allocating processor time so that when there are multiple jobs/applications running, each job is given processor time.

Question 16

Why is process scheduling important

Answer 16

Process as many jobs as possible in the least possible time.
Ensure all jobs are processed (fairly)
Maximise number of interactive user with fast response times.
Efficient use of resources/processor time

Question 17

When is time sharing used

Answer 17

In a multi- user system

Question 18

Describe round robin

Answer 18

processes are dispatched on a first in first out (FIFO) basis, with each job is given a limited amount of CPU time (time slice). At the end of the time slice the OS generates an interrupt at the end of the given time slice

Question 19

Describe First come first served

Answer 19

Jobs are processed in the order in which they arrive, with no system of priorities. May not be efficient as once a job starts it prevents other jobs from being processed. Also a job using a slow resource (eg printer) wastes processor time.

Question 20

Multilevel feedback queues

Answer 20

The algorithm creates several queues where jobs can move between them depending on how much processor time they use.

Question 21

Distributed operating system

Answer 21

A system which shares processing between the processors on a network. Used when there is a lot of data that needs to be processed quickly.

Question 22

Network Operating system

Answer 22

A network system allows a number of computers to share other resources at the same time.

Question 23

Facilities of Network Operating system

Answer 23

• File handling, allowing access and manipulation of files depending on the identity of the user
• Handling communication controls the movement of data around the network (by use of agreed protocol)
• Resource management ensures fair allocation of resources
• Automatic backup so that data is not lost if it is corrupted

Question 24

Multi-user

Answer 24

allows a number of users to use one computer at the same time. A single powerful mainframe/super computer (a large high-speed computer, supporting numerous workstations) is connected to lots of terminals (keyboard and display screen) all using the mainframe CPU.

Question 25

Real operating system

Answer 25

The system gives a response within a guaranteed time frame.

Question 26

Embedded operating system

Answer 26

Specialised OS for use in the computers built into larger systems. Found in all kinds of hardware.