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COMPUTER SCIENCE Flashcards

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1
Q

Algorithm

A

A sequence of instructions to compete a task.

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2
Q

Computer program

A

An implementation of an algorithm.

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3
Q

Decomposition

A

Breaking a problem down into sub-problems.

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4
Q

Efficiency

A

Comparison of time 2 algorithms take.

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5
Q

Binary Search

A

More efficient. Ordered array. Takes index at highest and lowest. It is compared to the midpoint. If the value is the midpoint it returns True. Else it looks at the upper or lower section and repeats. If 2 boundary indexes are equal it returns False.

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6
Q

Linear search

A

Less efficient. Searches across an entire array until the value is located. It requires more steps than binary.

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7
Q

Bubble Sort

A

Less efficient. Compares 2 values, if they aren’t in order they’re swapped. It moves along the array. May pass over multiple time until there are no swaps.

For 200 elements = 40000 Comparisons

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8
Q

Merge Sort

A

Breaks array down into individual elements and builds them back up into a sorted array.

For 200 elements = 1600 comparisons

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9
Q

Data Type

A

Range of values a variable can hold.

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10
Q

Identifier

A

Variable name. Describes it’s purpose.

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11
Q

Definite iteration

A

Loops for a known number of times.

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12
Q

Indefinite

A

Number of loops is unknown.

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13
Q

Selection

A

Branches code using Boolean logic.

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14
Q

Single branch selection

A

IF

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15
Q

2-branch selection

A

IF-ElSE

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16
Q

Multiple branch iteration

A

ELSE-IF

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17
Q

Nested iteration

A

Iteration within another iteration or selection.

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18
Q

Integer Division

A

DIV

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19
Q

Modulus

A

MOD

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20
Q

Data Strucures

A

Hold multiple related values in one place.

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21
Q

Index starts at..

A

0

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22
Q

2 dimensional array.

A

Arrays as elements of an array.

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23
Q

Subroutine

A

Block of code,

‘out of line’ : only runs when called upon.

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24
Q

Parameters

A

The value a subroutine takes.

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25
Q

Local variable

A

Only accessible in a subroutine.

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26
Q

Structured programming.

A

Using subroutines as part of decomposition.

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27
Q

Data validation routine

A

Ensure the user has entered a valid format or in correct range.

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28
Q

Test Data

A

The given values and compared with expected.

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29
Q

Normal Data

A

Everyday data,

Should be accepted, Not at boundary.

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30
Q

Boundary Data

A

At limits of what should and shouldn’t be accepted.

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31
Q

Erroneous Data

A

Should not be accepted, may also be boundary

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32
Q

Machine Code

A

Processors need code in this form to execute.

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33
Q

Assembly language.

A

Binary instructions given short words to represent. 1:1 relationship.

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34
Q

Assembler

A

Converts assembly language to machine code.

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35
Q

Processor families

A

Have their own specific assembly and machine code.

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36
Q

High-level language

A

Most commonly written in. Must be converted to low-level machine code. More expressive - shorter. Easily understood

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37
Q

Why write in low-level.

A

If a compiler does not exist for the hardware or you need high level control.

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38
Q

Compiler

A

On developers computer. Takes source code and converts to machine code for a specific processor family. Optimised and efficient. Hides original source code.

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39
Q

Interpreter.

A

Exists on the receiving computer. Converts line by line. Less optimised. Source code is visible. However more portable.

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40
Q

Hexadecimal

A

Uses placeholder of 16 and least significant of 1.

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41
Q

Bit

A

1 or 0

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42
Q

Byte

A

8 bits

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43
Q

Left shift

A

Multiply by 2.

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44
Q

Right shift.

A

DIV 2

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45
Q

Fixed-length character encodings

A

Universal way of encoding text. ASCII or UNICODE.

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46
Q

ASCII number of bits

A

7 bits

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47
Q

‘A’ in ASCII

A

65

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48
Q

Bitmap

A

Grid of pixels

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49
Q

Pixel

A

Smallest individual point of colour.

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50
Q

Resolution

A

Number of pixels used (width * height)

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51
Q

Colour Depth

A

Bits to encode a pixel

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52
Q

Analogue

A

Continuous data.

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53
Q

How analogue is converted to electrical signal.

A

Using a microphone.

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54
Q

Sample Rate

A

Number of samples per second. Measured in Hz.

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55
Q

Sample resolution

A

Bits to encode each level.

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56
Q

Compression

A

Making information take up less space.

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57
Q

Lossless compression.

A

None of original data is lost. RLE or Huffman coding.

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58
Q

RLE ideal situation

A

Repeating values

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59
Q

Where RLE may save space

A

Random data

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60
Q

Huffman coding guarantee

A

To never use more space than original.

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61
Q

Hardware

A

Physical components.

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62
Q

Software

A

Binary data that encodes instructions stored and executed on hardware.

63
Q

Computer system

A

Combination of software and hardware.

64
Q

Boolean Logic

A

Deals with expressions and systems with inputs and outputs. Can be True or False.

65
Q

Logic Circuit.

A

A system of logic gates.

66
Q

Application software.

A

Designed for User Interaction that performs a task.

eg. Web Browsers, word processors, games

67
Q

System Software

A

Provides a platform for application to run. May interact with user but directly with hardware.

eg. Operating System, utility programs.

68
Q

Operating System

A

Handles management of processor, memory, I/O, applications, security

69
Q

Memory stores..

A

Instructions and Data

70
Q

von Neumann architecture

A

Instructions and data are held in memory which can be accessed by processor.

71
Q

ALU

A

Arithmetic Logic Unit.

Evaluates arithmetic and logical expressions.

72
Q

Control Unit

A

Governs interface with input and output devices and when instructions and data are read or written.

73
Q

System Clock

A

Constant Pulse which regulates all of the fetch, decode, execute cycle.

74
Q

Bus

A

Physical connector between processor and memory and I/O devices which data is transferred.

75
Q

Fetching

A

Taking instructions to the processor.

76
Q

Execution

A

Instruction is executed: Calculate with ALU, read data from memory, write data

77
Q

Improving processor performance

A

Higher Clock Speed
More Cores
Cache

78
Q

Cores

A

Increases instructions executed simultaneously.

79
Q

Cache memory

A

Level 1: Attached on processor.
Level 2: Attached near processor.
Preloads frequently accessed results reducing time.

80
Q

Volatile

A

Doesn’t retain data when power is taken away.

81
Q

Secondary data

A

Persistent even without electrical power. Can’t communicate directly with processor so must move to main memory.

82
Q

Main memory

A

Communicates directly with processor although volatile.

83
Q

RAM

A

Random Access Memory. Emptied upon start-up.

84
Q

ROM

A

Read Only Memory. OS must be loaded into RAM. Contains persistent memory to start up computer system them OS will take over.

85
Q

Embedded System

A

Memory and Storage in one place. All instructions on ROM as their single purpose,

86
Q

Magnetic Media mechanism

A

Magnet on the end of the laterally moving arm can detect the polarity of a sector of the platter below. It can interpret this as a 0 or 1. It can change the polarity to write data.

87
Q

Optical media mechanism

A

A laterally moving arm contains a laser. It is aimed at the disk containing pits and lands. It is either reflected or not. This can be interpreted as a 1 or 0.

88
Q

Solid State Drive mechanism

A

No moving parts, uses large electrical circuits to store data.

89
Q

Magnetic Media: pros/cons

A

Pros:
Low cost per Byte
Faster read/write than optical

Cons:
Uses moving parts so it is vulnerable and less portable.

90
Q

Optical Media: pros/cons

A

Pros:
Distribute data without network

Cons:
Low capacity
Vulnerable to damage. 
Slow read speed
Very slow write speed
91
Q

Solid state : pros / cons

A 
Pros:
Very fast read/write 
No moving parts, robust
More efficient (energy)
Smaller size per bit

Cons:
High cost per Byte

92
Q

Cloud Storage

A

Data stored elsewhere in large data centres. Accessed through internet connection across multiple devices. Trust is held with the company for privacy and distribution. They can be hacked or unauthorised access can be gained.

93
Q

Computer Network

A

2 or more devices which can communicate

94
Q

Benefits of Computer Networks

A 
Allows sharing of data between devices.
Resources to be shared. eg. Printers.
Enable collaborative working.
Access to global resources eg. World Wide Web
...
95
Q

Risks of a Computer Network

A

Increased risk of unauthorised access.
Expensive creation and maintenance. (Although outweighed by benefits)
Centralises organisation’s data to few devices making it easier to target.

96
Q

PAN

A

Personal Area Network
Usually Bluetooth.
Centred around one person.
Eg. Smartphone, wireless headphones, mouse.

97
Q

LAN

A

Local Area Network.
Small geographic area: eg. Office or classroom.
Owned and controlled by one person or organisation.
Often connect to the internet.

98
Q

WAN

A 
Wide Area Network.
Wide geographic area.
eg. Internet
Collective ownership and usage is leased to organisations.
Connected LANs
99
Q

Wired Network

A

Using
Copper Wires: Already widely installed.
Fibre Optics: faster, higher capacity, used where installed.

100
Q

Wireless Network options.

A

A computer network without the use of wires.

101
Q

Wired Network properties

A

Always use full connection potential of wire.
Only open to physically connected devices increasing security.
Network speeds are regulated.
Devices can only be added where physically cabling allows.

102
Q

Wireless Network properties

A

Devices can only send data one-at-a-time so must wait.
Using MAC address filtering allowed devices can be specified although limits ‘guest’ access.
Devices can be moved within radius of connection.
Open to more unauthorised access.
Network speeds can drop if many devices are connected.

103
Q

Topology

A

The way devices are connected in a network.

104
Q

Star Topology pros

A

If one device fails the network is unaffected.
Simple to add new users.
Each device can simultaneously transmit data at full speed.

105
Q

Star topology cons

A

Expensive switch and if there are many users.

If the switch is affected the whole network is affected.

106
Q

Bus topology pros

A

Aren’t dependent on switch.
Cheaper short wiring.
The whole network isn’t affected in a single connection issue.

107
Q

Bus topology cons

A

Data collisions, data must resent slowing down speeds.
More Devices = More Collisions
If the cable is broken the network becomes split. As there aren’t a terminator at both ends data will reflect shutting down a network.

108
Q

Protocol

A

Agreed way to communicate data.

109
Q

TCP/IP Stack

A

Simplified layers of the internet. All sent data passes down 4 layers it is they routed across the internet and works back up the stack on receiving.

110
Q

Transport Layer

A

Takes data and segments it into packers (may be numbered).

111
Q

Network layer

A

Stamps each packet with IP addresses of sender and the destination.

112
Q

(Data) Link layer

A

Bottom layer used to physically send packet across the network.

113
Q

Ethernet

A

Family of protocols for LAN data transmission.

114
Q

Wi-Fi

A

Family of protocols for wireless data transmission

115
Q

TCP

A

Transmission Control Protocol.
Transport Layer.
Segments data into numbered packets. Ensures all packets arrive and not corrupted.

116
Q

UDP

A

User Datagram Protocol
Transport Layer.
Segments packets into numbered packets but doesn’t ensure all arrive or corrupted.

117
Q

IP

A

Internet Protocol
Network Layer.
Stamps source and destination IP onto packets to route each packet correctly.

118
Q

HTTP

A

HyperText Transfer Protocol

Application layer protocol for transferring
web pages.

119
Q

HTTPS

A

HyperText Transfer Protocol Secure.
Application layer.
Protocol for transferring encrypted web pages.

120
Q

FTP

A

File Transfer Protocol.
Application layer.
Protocol for transferring files.

121
Q

SMTP

A

Simple Mail Transfer Protocol.
Application layer.
Protocol for sending emails.

122
Q

IMAP

A

Internet Message Access Protocol
Application Layer.
Protocol for retrieving emails.

123
Q

Security

A

Preventing unauthorised access to data. Also covers encryption.

124
Q

Authentication

A

Requires user to provide credentials such as username or password.

125
Q

Encryption

A

Taking plaintext and translating it into meaningless cipher-text. A key is required to decode. Used when transmitting sensitive information.

126
Q

Firewall

A

Combines Hardware and Software. Inspects incoming packets and assesses their likelihood of being malicious.

127
Q

MAC address

A

Media Access Control. Unique to every Network Interface Card. A network can use blacklisting or whitelisting to filter access.

128
Q

Social Engineering

A

Manipulating people so that they give up confidential

information.

129
Q

Blagging (pretexting)

A

Creating an invented scenario engage a targeted victim.

130
Q

Phishing

A

Using SMS or email to obtain private information. Often contain a hyperlink resulting in malware or handing over private information.
Spear Phishing is targeted towards an individual.

131
Q

Pharming

A

Cyberattack intended to redirect a website’s traffic to a fake version. Can be performed by changing files on the computer that associates the URL and IP (on the specific computer).
Or it could attack DNS which is the service associates URLs and IP (before it reaches a computer)(entire domain)

132
Q

Shouldering

A

Physically observing private information over their shoulder.

eg. PIN number

133
Q

Malware / malicious code

A

Hostile or intrusive software

134
Q

Computer Virus

A

Replicates itself and inserts code into other programs infecting the computer system.
Spread using social engineering or system vulnerabilities.

135
Q

Reasons for creating a virus

A

Making Money eg. Ransomware
Political Statement
Curiosity or Vandalism
Sabotage or as a “zombie” in a DDoS attack.

136
Q

Trojan

A

Software which pretends to be legitimate but contains malware. Don’t infect other programs but provide a ‘back door’ into the computer system.
Usually spread using social engineering.

137
Q

Spyware

A

Gains information about user without their knowledge.
Adware
Tracking cookies on webpages
Key loggers
Web beacons- sends small amounts of data of how the user interacts with webpages.

Spread through social engineering.

138
Q

Adware

A

Displays advertising using web pages and applications that generate their revenue through advertising.
It may be targeted towards the users browsing history or shopping habits.
It’s malware if its unwanted or it uses information which has been generated illegally.

139
Q

Biometric Measures

A 
Fingerprints
Face recognition
Iris scanning
Retina Scanning
Hand geometry
140
Q

Password Systems

A

Passwords are stores securely in the form of a ‘hash’. Which encrypts the password so it’s not explicitly stored. As if it’s compromised it would be a large security risk.

141
Q

CAPTCHA

A

Distinguishes bots from people. Usually graphical puzzles which are simple for humans but difficult for programs without good AI.

142
Q

Email Confirmation

A

2-step authentication. Uses secondary source of information to ensure their human and it’s a legitimate email.

143
Q

Automatic Software Updates

A

Combats attacks on outdated software with vulnerabilities. Operating Systems are the primary target as for their direct control over network connections. When a vulnerability is found they will ‘patch’ it. Counterfeit operating systems are vulnerable as they can’t download updates.

144
Q

Penetration Testing

A

Allowing an organised team to attempt to gain access to an organisations network.
Team of white hat crackers are hired to simulate a black hat attack.
They evaluate strengths and weaknesses.

145
Q

White-box penetration testing

A

Crackers have insider knowledge of the system. Simulates a malicious insider.

146
Q

Black-box penetration testing

A

No prior knowledge. Simulates malicious outsider.

147
Q

Mobile Technologies

A

Collect data on:
Number of calls, who to, time and location
Location of person using GPS
Applications that access users’ data beyond what’s necessary.
Web browsing information and history.

Phones are rapidly replaced increases demand for metals and plastics. 2 year contracts mean safe disposal.

148
Q

Wireless Technology

A

Can use passwords to limit connections.
MAC address filtering: use it whitelisting and blacklisting
Networks can use encryption to ensure security as the signal can be picked up by anything within radius.
Public networks can collect data about devices and webpages accessed also who is responsible for the material that a user chooses to access.

149
Q

Theft of Computer Code

A

If stolen other groups can make profit from another organisations work.
Can be stolen by:
An insider, crackers accessing company’s computer system.
Can be reduced with use of penetration testing.

150
Q

Algorithm Copyright

A

It isn’t possible to copyright an algorithm. But it is possible to copyright an implementation of an algorithm. Therefore it is possible to use copyright against using source code without permission.
It is only as strong as countries regulate them, many countries are more relaxed therefore not protected.

151
Q

Cracking and Hacking

A

Hacking is LEGAL. It is the process of changing or amending code. eg. Hacking a game for bonuses. Hacking being illegal is a media misconception. It is largely ethically sound and legal.

Cracking is ILLEGAL. It is the unauthorised access to computers, networks, data. It is only legal under white-hat penetration testing. Carried out for:
Money, vandalism, curiosity or espionage.

They use software tools and social engineering to target systems.

152
Q

Wearable technology

A

Eg. Google Glass shows concept. Can be used for safety purposes such as GPS transmitter for locating people in an avalanche.

Privacy issues:
The more data collected is more data to be stolen.
Eg. Google Glass camera could be used without the users consent or knowledge.

153
Q

Computer-based implant.

A

Can improve health and quality of life.
Eg. Cochlear implants enable deaf people to hear.
Eg. Network aware pacemakers although may be cracked putting lives at risk.

Computer Science (3 decks)

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