Computer Science Paper 1 > 1.2.1 - Systems Software > Flashcards

1.2.1 - Systems Software Flashcards

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1
Q

Operating system definition

A

Special type of system software that provides an interface between the user and the computer

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2
Q

Functions of the OS

A

Memory management
Resource management
Interrupt handling
I/O management
Utility software
Security
User Interface

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3
Q

Memory management purpose

A

Deal with allocation and deallocation of memory (finite resource)

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4
Q

3 methods of memory management

A

Paging
Segmentation
Virtual Memory

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5
Q

Paging

A

Splitting memory into equal sized chunks
- Fixed size
- Physical divisions of data

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6
Q

Advantages of paging

A

Works well with virtual memory

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7
Q

Disadvantages of paging

A

Internal fragmentation leads to wasted space
Non-contiguous storage

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8
Q

Segmentation

A

Splitting memory into variable sized chunks
- Variable size
- Logical divisions of data

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9
Q

Segmentation advantages

A

Contiguous storage

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10
Q

Segmentation disadvantages

A

Doesn’t work well with virtual memory
External fragmentation wastes space

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11
Q

Virtual memory

A

The CPU uses a section of secondary storage when RAM is insufficient
- Sections of programs not currently in use get moved to virtual memory

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12
Q

Virtual memory advantages

A

Allows continued function when RAM is full
Cheaper than getting more RAM

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13
Q

Virtual memory disadvantages

A

Much slower access times than RAM
Disk thrashing - too much time wasted swapping data/instructions

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14
Q

Resource management

A

Deciding which tasks to process, for how long and in what order - done using scheduling algorithms

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15
Q

Objective of scheduling

A

Maximising throughput and giving each task a fair amount of processing time

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16
Q

Preemptive algorithm

A

Allocates the CPU for given time slice
Allows for interruption of processes

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17
Q

Non-preemptive

A

Allocates the CPU to a process which has control until completed/waiting
No interruptions allowed

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18
Q

Examples of preemptive algorithms

A

Multi-level feedback queues
Shortest remaining time
Round robin

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19
Q

Examples of non-preemptive algorithms

A

First come first served, shortest job first

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20
Q

Three states of a process

A

Running - has control of CPU
Ready-to-run - in queue waiting for time slice
Blocked - waiting for I/O operation

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21
Q

Round robin description

A

Equally distributes processor time among all processes

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22
Q

FCFS description

A

The process being worked on will have control of CPU until it completes or switches to waiting

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23
Q

Multi level feedback queues description

A

Shorter and more critical tasks are processed first. Multiples queues used so tasks of equal size are grouped together

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24
Q

Shortest job first

A

Processes continually sorted in queue so shorter jobs are at the front

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25
Shortest remaining time
Specific time slice set and if task does not complete in time it joins the back of the queue. Task with shortest remaining time is at the front of the queue
26
Round robin advantages
Fair Predictable
27
Round robin disadvantages
Choosing right time slice can be difficult Lots of waiting for long processes
28
FCFS advantages
Fair
29
FCFS disadvantages
Poor performance if long processes hog CPU High-priority tasks may have to wait
30
Multi level feedback queues advantages
Smaller tasks prioritised Uses prioritisation queues
31
Multi level feedback queues disadvantages
More complex Setting correct parameters for queues can be complex
32
Shortest job first advantages
Minimises waiting time Efficient for short processes
33
Shortest job first disadvantages
Requires knowing how long a process has left in advance Long processes can be starved
34
Shortest remaining time advantages
Good for short jobs Preemptive so allows for best CPU usage
35
Shortest remaining time disadvantages
Requires time left of process to be known in advance
36
5 types of OS
Distributed, embedded, multi-user, multi-tasking, real time
37
Distributed OS description
Run across multiple devices, allowing processing load to be spread across multiple processors (pooling resources)
38
Distributed OS uses
Servers
39
Embedded OS description
Perform a small range of specific tasks - catered towards a specific device (much less power usage)
40
Embedded OS uses
Raspberry Pi
41
Multi-tasking OS description
Enables user to carry out multiple tasks at the same time
42
Multi-tasking OS uses
General purpose computers (Windows, MacOS)
43
Multi-user OS description
Multiple users making use of one computer
44
Multi-user OS uses
Supercomputers
45
Real time OS description
Perform tasks within a guaranteed time frame with built in redundancy
46
Real time OS uses
Self-driving cars
47
BIOS
Basic Input Output System - first software to run when system starts
48
Step one of booting process
Power on (hardware button) and wait for current to stabilise
49
Step two of booting process
Hardware reset signal sent along control bus to PC
50
Step three of booting process
PC updated to contain address (in ROM) of BIOS
51
Step four of booting process
POST is run (power on self test)
52
Step five of booting process
POST is passed
53
Step six of booting process
Bootstrap loads parts of OS (inc. kernel) from secondary storage into RAM
54
Step seven of booting process
Boot file loads personalisation features and user settings
55
Device driver definition
A special type of systems software that enables OS to control and interact with hardware devices
56
Device driver use
App needs access to a device OS calls function implemented by driver Driver can communicate with hardware of device Driver gives data back to app
57
Utility software
58
Security
59
User interface
60
Virtual machine definition
When software is used to emulate a machine
61
Computer Science Paper 1
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