1.2.1 - systems software

Question 1

operating system

Answer 1

Controls the hardware and software of a computer system and provides a user interface.

Question 2

Name the 5 types of operating systems.

Answer 2

1. multi-tasking
2. multi-user
3. distributed
4. embedded
5. real-time

Question 3

multi-tasking OS

Answer 3

Each active program is scheduled to receive a slice of processing time in quick rotation, giving the impression they are operating at the same time.

Question 4

multi-user OS

Answer 4

Allows more than one person to use a computer at the same time.

Question 5

distributed OS

Answer 5

Combines the processing power of multiple computers across a network for a single task.

Question 6

embedded OS

Answer 6

Tend to run on dedicated hardware so they run with maximum efficiency, using low-powered processors and very little memory.

Question 7

real-time OS

Answer 7

Processes have to be guaranteed to execute within a known time frame.

Question 8

Basic Input Output System (BIOS)

Answer 8

Responsible for loading the OS when the computer first turns on. Initialises and tests the system hardware components.

Question 9

bootstrap

Answer 9

Used to load the OS kernel into memory.

Question 10

device driver

Answer 10

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

Question 11

virtual machine

Answer 11

A program that has the same functionality as a physical computer.

Question 12

5 functions of an operating system

Answer 12

1- memory management
2- interrupt service routines
3- processor scheduling
4- backing store management
5- management of all input and output

Question 13

paging

Answer 13

• memory is split into pages of size 4Kb each
• a process currently in memory may be held in several non-contiguous pages
• a page table uses mapping to store a link between the physical memory address and the logical address space of each process

Question 14

segmentation

Answer 14

The logical division of address space into varying length segments based on the program’s structure.

Question 15

interrupt

Answer 15

A signal from a software program, hardware device or internal clock to the CPU.

Question 16

When does a software interrupt occur?

Answer 16

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

Question 17

example of a hardware interrupt

Answer 17

‘printer out of paper’

Question 18

interrupt service routines

Answer 18

• suspends execution of running process
• disables interrupts of a lower priority
• puts values of registers onto system stack
• interrupt service routine is called

Question 19

4 objectives of a scheduler

Answer 19

1- maximise output
2- be fair to all users on a multi-user system
3- provide acceptable response time to all users
4- ensure hardware resources are kept as busy as possible

Question 20

round robin scheduling

Answer 20

Each process is given a time slice controlled by an interval timer. If the process does not complete before its time expires, the despatcher gives the CPU to the next process. Guarantees a reasonable response time for all users.

Question 21

first come first served scheduling

Answer 21

Jobs are processed in the order in which they arrive. No system of priorities.

Question 22

shortest remaining time scheduling

Answer 22

The process with the smallest estimated time to completion is run next. However, it requires knowledge of how long a job will take. Possible for batch jobs like payroll.

Question 23

shortest job first scheduling

Answer 23

The process with the smallest estimated running time is run next.

Question 24

multi-level feedback queues scheduling

Answer 24

This algorithm is designed to:
- give preference to short jobs
- give preference to I/O bound processes
- separate processes into categories based on their need for the processor