1.2.1 Systems Software

Question 1

What is an operating system?

Answer 1

A program that manages the operations of the computer for the user in order to act as a bridge between the hardware and the user.

Question 2

What are the six functions an operating system performs?

Answer 2

Providing a user interface
Memory management
Handling interrupts
Processor scheduling
Provide security.
Management of all I/O.

Question 3

What are the two memory management techniques?

Answer 3

Paging and segmentation.

Question 4

How does paging work?

Answer 4

Memory is divided into “pages” of 4kb each, a program can be stored in several non-contiguous pages. A page table uses mapping to store the link between the physical and logical page locations.

Question 5

How does segmentation work?

Answer 5

Memory is divided logically into segments according to its contents.

Question 6

What is an interrupt?

Answer 6

A signal from software, hardware, internal clock or peripherals.

Question 7

Why does a software interrupt happen?

Answer 7

When an application terminates or requests certain services from the OS.

Question 8

Why might a hardware interrupt happen?

Answer 8

A hardware interrupt will occur when an I/O operation is complete or an error arises.

Question 9

If there are no errors and nothing being completed or terminated why might an interrupt still take place?

Answer 9

Interrupts are triggered regularly by a timer in order to interrupt a process to allow the next process to have processor time.

Question 10

What happens when the CPU receives an interrupt?

Answer 10

The CPU suspends the current process and disables all interrupts of a lower priority. it then clears the program counter and all other registers by sending their values into the system stack. and the appropriate ISR is called to deal with the issue.

Question 11

What is an example of a high priority interrupt?

Answer 11

Power-fail interrupt.

Question 12

What is an example of a low priority interrupt?

Answer 12

I/O operation termination.

Question 13

When does the test for interrupt presence occur in the fetch decode execute cycle?

Answer 13

at the end, if the presence is detected then control is transferred to the appropriate ISR.

Question 14

What does multitasking mean?

Answer 14

A single processor computer carrying out small parts of multiple larger tasks to give the appearance of simultaneous processing.

Question 15

What are the objectives of the scheduler?

Answer 15

Maximise throughput
Be fair to all users
Provide acceptable response time for users
Ensure hardware is in as much use as possible.

Question 16

What are the five scheduling algorithms?

Answer 16

RR - Round robin
FCFS - First come first serve
SJF - Shortest job first
SRT - Shortest remaining time
Multilevel feedback queues.

Question 17

How does RR work?

Answer 17

Processors are dispatched in a first in first out basis, each process is given the same time slice with the processor, regardless whether the process has been completed or not, the next process will be given its time slice, this continues until the processes have been finished.

Question 18

How does FCFS work?

Answer 18

Jobs are processed in the order in which they arrive in their entirety.

Question 19

How does SJF work?

Answer 19

The process with the smallest estimated time is run next.

Question 20

How does SRT work?

Answer 20

The process with the smallest estimated time is run next since that will always be the one currently executing processes will be completed in full.

Question 21

How do multilevel feedback queues work?

Answer 21

The algorithm implements multiple queues all with their own scheduling algorithm and each queue is organised based on priority.

Question 22

What are the five types of OS?

Answer 22

Distributed
Embedded
Multitasking
Multi-user
Real-time

Question 23

What is a distributed OS?

Answer 23

A form of parallel processing which spreads a workload over multiple servers but appears to the user as if it were a single system handling the workload.

Question 24

What is a real-time OS?

Answer 24

An operating system designed to give a response within a guaranteed time frame

Question 25

What is an embedded OS?

Answer 25

An OS with a minimal user interface used to control devices based on input from sensors.

Question 26

What is a multitasking OS?

Answer 26

An OS that allows the user to run multiple programs at once and can switch between them to give the appearance only one is running.

Question 27

What does BIOS stand for?

Answer 27

Basic Input Output System.

Question 28

Where is the BIOS stored?

Answer 28

EPROM.

Question 29

What is the purpose of the BIOS?

Answer 29

To initialise the PC and to test the system hardware as well as to load the operating system from the hard disk to RAM.

Question 30

What is a device driver?

Answer 30

A computer program that provides a software interface to a particular piece of hardware.

Question 31

What is the point of a device driver?

Answer 31

It enables operating systems to control new hardware without needing to know the full details of the hardware in question.

Question 32

Define a virtual machine plus a fact.

Answer 32

Any instance where software is used to take on the function of the machine. Code running on a VM tends to be slower than compiled.