1.2 Software and software development

Question 1

What is an operating system?

Answer 1

a collection of programs that provide an interface between user and computer.

Question 2

What features do operating systems provide?

Answer 2

Memory management; Resource management; file management; input/output management; interrupt management; utility software; security; user interface.

Question 3

What is memory management?

Answer 3

How the memory in the RAM is divided and identified by paging, segmentation and virtual memory

Question 4

What is paging?

Answer 4

Splitting memory into equal sized physical divisions called pages.

Question 5

What is segmentation?

Answer 5

Splitting memory into logical divisions called segments that represent the structure and flow of the program.

Question 6

What are the similarities of paging and segmentation?

Answer 6

They allow the programs to efficiently use space in memory

Question 7

What are the differences of paging and segmentation?

Answer 7

Pages are fixed size and fit into sections of memory , segments vary in size and are made of complete sections of memory.

Question 8

What dose virtual memory do?

Answer 8

it uses a section of the hard drive acts as RAM when main memory doesn’t have enough space. sections of the program not currently in use are temporally moved to virtual memory.

Question 9

Whats the downside to using virtual memory excessively?

Answer 9

Disk thrashing; when pages are being swapped between hard disk and main memory, as it takes a long time to transfer them.

Question 10

What is resource managment?

Answer 10

scheduling

Question 11

What is Scheduling?

Answer 11

Allowing sections of programs to be run and receive a fair amount of processing charity.

Question 12

What are the two types of scheduling algorithms?

Answer 12

Pre-emptive and Non pre-emptive.

Question 13

What are pre-emptive algorithms?

Answer 13

jobs are actively started or stopped by the operating system.
E.g. multilevel feedback queues, shortest remaining time, round robin

Question 14

What are Non pre-emptive algorithms?

Answer 14

Once a job is started, it is left alone until it is completed
E.g. first come first served, shortest job first

Question 15

What is the Round robin Scheduling algorithms?

Answer 15

each job has a section of processor time within which it is allowed to execute. longer jobs will take longer and job priority will not be taken into account.

Question 16

What is the first come first serve scheduling algorithm?

Answer 16

Jobs are processed in chronological order. easy to implement, but doesn’t take priority into account.

Question 17

What is the multilevel feedback queues scheduling algorithm?

Answer 17

makes use of multiple queues which are ordered per priority, this is difficult to implement

Question 18

What is the shortest job first scheduling algorithm?

Answer 18

The jobs are ordered according completion time, longest jobs being completed at the end. this is beneficial to batch systems, but requires processor to calculate how long each job will take

Question 19

What is processor starvation?

Answer 19

When a particular process doesn’t receive enough processor time in order to execute and be completed.

Question 20

What is the shortest remaining time scheduling algorithm?

Answer 20

the queue is processed in order of time left from completion.

Question 21

What are interrupts?

Answer 21

signals generated by software or hardware to indicate to the processor that a process needs attention.

Question 22

How are interrupts stored?

Answer 22

in a priority queue in an interrupt register

Question 23

How are interrupts serviced?

Answer 23

the interrupt service routine; if there is a interrupt with higher priority than current process, the current process are put in a stack. the processor loads the appropriate interrupt service routine and the flag is set. once processed the flag is reset interrupt queue checked before transferring the stack back into processors.

Question 24

What are the different processes of the operating system?

Answer 24

Distributed; Embedded; Multi-tasking;
Multiuser; Real time

Question 25

What is a distributed operating system?

Answer 25

a type of OS that runs across multiple devices and allows the load to be spread across multiple processors.

Question 26

What is a embedded operating system?

Answer 26

Devices built for a small range of specific tasks, with limited in their functionality and low power usage

Question 27

What is a multi-tasking operating system?

Answer 27

a OS that allows the user to carry out task seemingly simultaneously, though time slicing quickly switching between programs and applications in memory.

Question 28

What is a multi-tasking operating system?

Answer 28

when multiple users make use of one computer (normally supercomputer), needs a scheduling algorithm.

Question 29

What is a real time operating system?

Answer 29

an OS designed to performs a task within a guaranteed time frame, used in time-critical computer systems.