1.2.1 Systems Software

Question 1

Officially recognised application packages:

Answer 1

Word Processor
Database software
Presentation software
Email software
Graphics manipulation
Web browser

Question 2

Operating System Features

Answer 2

Provide utilities: File encryption, defragmentation, backups
Provide user interface
Security: Virus scanning, firewall, file encryption
File management
Resource management
Interrupt management

Question 3

Memory Management

Answer 3

Paging:
CHUNKING into equal sized blocks
Enables virtual memory
Pages not in active use will be taken away
Internal fragmentation: Free space in each allocated blocks

Segmentation:
CHUNKING based on logical sized divisions
Represents the structure and flow of program
External fragmentation: Arrangement of data becomes more fragmented over time

Question 4

Virtual Memory

Answer 4

Section of secondary storage acts as RAM
Sections NOT BEING USED offloaded by OS to VM
Frees up memory for other programs
DISK THRASHING: Comp freezes due to pages being swapped too much

Question 5

Interrupt examples and types:

Answer 5

Hardware failure
External device failure
Software interrupts
Hardware interrupts
Trap interrupts

Question 6

Dealing with an Interrupt:

Answer 6

Checked for at start and end of FDE cycle
If interrupts is lower priority then continue normally
Flag used to determine if interrupt is enabled
If so contents of registers copied to stack
Program Counter set to point to ISR, ISR runs
Previous register values copied back
Flag is reset
If higher priority interrupt this is added to the stack

Question 7

Round Robin

Answer 7

() Each job is given a TIME SLICE which is a section of processor time
() Once that job is completed the program is given another slice
() Completed jobs are removed

+ All jobs attended to

• Does not take into account

Question 8

First come first served

Answer 8

Processed chronologically

+ Straightforward to implement
- Does not take priority into account

Question 9

Multilevel feedback queue

Answer 9

Multiple queues ordered based on different priority

+ Considers priority

• Difficult to implement

Question 10

Shortest Job First

Answer 10

Ordered based on time required
Longest jobs serviced at the end

+ Suited to batch systems as waiting time is reduced

• Processor starvation if short jobs are continuously added

Question 11

Shortest time remaining

Answer 11

Ordered based on time left

+ Throughput is increased as shorter processes can be quickly completed

• Does not take into account urgency

Question 12

Types of OS

Answer 12

Distributed: Multiple machines make single unit
Embedded
Multi-tasking: Access multiple tasks concurrently
Multi-user
Real-time: Immediate data processing

Question 13

BIOS

Answer 13

() First program that runs
() Settings stored in RAM
() Series of tests
() Power-On-Self-Test: Hardware components are working
() Checks CPU clock, memory and processor
() Tests external memory devices
() Starts bootstrap loading sequence

Question 14

Device Drivers

Answer 14

Programs that allow OS to interact with hardware
Specific to computers architecture
Specific to operating system

Question 15

Virtual Machines

Answer 15

“A theroetical computer and a software implementation of a computer system.
Provies an environment with a translate to intermediate code to run”

Structure:
Hardware
OS
Hypervision
Virtual Machine
Application

Virtual Machine Eval:
+ Cross-platform compatibility
+ Isolated test environments (no other programs running)
+ Virus testing
- Can exhaust host OS

Question 16

Intermediate Code

Answer 16

Halfway between source and object code.
Independent of processor achitecture so it can run across difference machines.
Takes longer to execute

Question 17

Virtual machine uses

Answer 17

Test programs
Protection from malware
Running software compatible with different types of OS