COMPUTER SCIENCE Flashcards
1
Q
Algorithm
A
A sequence of instructions to compete a task.
2
Q
Computer program
A
An implementation of an algorithm.
3
Q
Decomposition
A
Breaking a problem down into sub-problems.
4
Q
Efficiency
A
Comparison of time 2 algorithms take.
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.
6
Q
Linear search
A
Less efficient. Searches across an entire array until the value is located. It requires more steps than binary.
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
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
9
Q
Data Type
A
Range of values a variable can hold.
10
Q
Identifier
A
Variable name. Describes it’s purpose.
11
Q
Definite iteration
A
Loops for a known number of times.
12
Q
Indefinite
A
Number of loops is unknown.
13
Q
Selection
A
Branches code using Boolean logic.
14
Q
Single branch selection
A
IF
15
Q
2-branch selection
A
IF-ElSE
16
Q
Multiple branch iteration
A
ELSE-IF
17
Q
Nested iteration
A
Iteration within another iteration or selection.
18
Q
Integer Division
A
DIV
19
Q
Modulus
A
MOD
20
Q
Data Strucures
A
Hold multiple related values in one place.
21
Q
Index starts at..
A
0
22
Q
2 dimensional array.
A
Arrays as elements of an array.
23
Q
Subroutine
A
Block of code,
‘out of line’ : only runs when called upon.
24
Q
Parameters
A
The value a subroutine takes.
25
Local variable
Only accessible in a subroutine.
26
Structured programming.
Using subroutines as part of decomposition.
27
Data validation routine
Ensure the user has entered a valid format or in correct range.
28
Test Data
The given values and compared with expected.
29
Normal Data
Everyday data,
| Should be accepted, Not at boundary.
30
Boundary Data
At limits of what should and shouldn’t be accepted.
31
Erroneous Data
Should not be accepted, may also be boundary
32
Machine Code
Processors need code in this form to execute.
33
Assembly language.
Binary instructions given short words to represent. 1:1 relationship.
34
Assembler
Converts assembly language to machine code.
35
Processor families
Have their own specific assembly and machine code.
36
High-level language
Most commonly written in. Must be converted to low-level machine code. More expressive - shorter. Easily understood
37
Why write in low-level.
If a compiler does not exist for the hardware or you need high level control.
38
Compiler
On developers computer. Takes source code and converts to machine code for a specific processor family. Optimised and efficient. Hides original source code.
39
Interpreter.
Exists on the receiving computer. Converts line by line. Less optimised. Source code is visible. However more portable.
40
Hexadecimal
Uses placeholder of 16 and least significant of 1.
41
Bit
1 or 0
42
Byte
8 bits
43
Left shift
Multiply by 2.
44
Right shift.
DIV 2
45
Fixed-length character encodings
Universal way of encoding text. ASCII or UNICODE.
46
ASCII number of bits
7 bits
47
‘A’ in ASCII
65
48
Bitmap
Grid of pixels
49
Pixel
Smallest individual point of colour.
50
Resolution
Number of pixels used (width * height)
51
Colour Depth
Bits to encode a pixel
52
Analogue
Continuous data.
53
How analogue is converted to electrical signal.
Using a microphone.
54
Sample Rate
Number of samples per second. Measured in Hz.
55
Sample resolution
Bits to encode each level.
56
Compression
Making information take up less space.
57
Lossless compression.
None of original data is lost. RLE or Huffman coding.
58
RLE ideal situation
Repeating values
59
Where RLE may save space
Random data
60
Huffman coding guarantee
To never use more space than original.
61
Hardware
Physical components.
62
Software
Binary data that encodes instructions stored and executed on hardware.
63
Computer system
Combination of software and hardware.
64
Boolean Logic
Deals with expressions and systems with inputs and outputs. Can be True or False.
65
Logic Circuit.
A system of logic gates.
66
Application software.
Designed for User Interaction that performs a task.
eg. Web Browsers, word processors, games
67
System Software
Provides a platform for application to run. May interact with user but directly with hardware.
eg. Operating System, utility programs.
68
Operating System
Handles management of processor, memory, I/O, applications, security
69
Memory stores..
Instructions and Data
70
von Neumann architecture
Instructions and data are held in memory which can be accessed by processor.
71
ALU
Arithmetic Logic Unit.
| Evaluates arithmetic and logical expressions.
72
Control Unit
Governs interface with input and output devices and when instructions and data are read or written.
73
System Clock
Constant Pulse which regulates all of the fetch, decode, execute cycle.
74
Bus
Physical connector between processor and memory and I/O devices which data is transferred.
75
Fetching
Taking instructions to the processor.
76
Execution
Instruction is executed: Calculate with ALU, read data from memory, write data
77
Improving processor performance
Higher Clock Speed
More Cores
Cache
78
Cores
Increases instructions executed simultaneously.
79
Cache memory
Level 1: Attached on processor.
Level 2: Attached near processor.
Preloads frequently accessed results reducing time.
80
Volatile
Doesn’t retain data when power is taken away.
81
Secondary data
Persistent even without electrical power. Can’t communicate directly with processor so must move to main memory.
82
Main memory
Communicates directly with processor although volatile.
83
RAM
Random Access Memory. Emptied upon start-up.
84
ROM
Read Only Memory. OS must be loaded into RAM. Contains persistent memory to start up computer system them OS will take over.
85
Embedded System
Memory and Storage in one place. All instructions on ROM as their single purpose,
86
Magnetic Media mechanism
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
Optical media mechanism
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
Solid State Drive mechanism
No moving parts, uses large electrical circuits to store data.
89
Magnetic Media: pros/cons
Pros:
Low cost per Byte
Faster read/write than optical
Cons:
Uses moving parts so it is vulnerable and less portable.
90
Optical Media: pros/cons
Pros:
Distribute data without network
```
Cons:
Low capacity
Vulnerable to damage.
Slow read speed
Very slow write speed
```
91
Solid state : pros / cons
```
Pros:
Very fast read/write
No moving parts, robust
More efficient (energy)
Smaller size per bit
```
Cons:
High cost per Byte
92
Cloud Storage
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
Computer Network
2 or more devices which can communicate
94
Benefits of Computer Networks
```
Allows sharing of data between devices.
Resources to be shared. eg. Printers.
Enable collaborative working.
Access to global resources eg. World Wide Web
...
```
95
Risks of a Computer Network
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
PAN
Personal Area Network
Usually Bluetooth.
Centred around one person.
Eg. Smartphone, wireless headphones, mouse.
97
LAN
Local Area Network.
Small geographic area: eg. Office or classroom.
Owned and controlled by one person or organisation.
Often connect to the internet.
98
WAN
```
Wide Area Network.
Wide geographic area.
eg. Internet
Collective ownership and usage is leased to organisations.
Connected LANs
```
99
Wired Network
Using
Copper Wires: Already widely installed.
Fibre Optics: faster, higher capacity, used where installed.
100
Wireless Network options.
A computer network without the use of wires.
101
Wired Network properties
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
Wireless Network properties
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
Topology
The way devices are connected in a network.
104
Star Topology pros
If one device fails the network is unaffected.
Simple to add new users.
Each device can simultaneously transmit data at full speed.
105
Star topology cons
Expensive switch and if there are many users.
If the switch is affected the whole network is affected.
106
Bus topology pros
Aren’t dependent on switch.
Cheaper short wiring.
The whole network isn’t affected in a single connection issue.
107
Bus topology cons
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
Protocol
Agreed way to communicate data.
109
TCP/IP Stack
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
Transport Layer
Takes data and segments it into packers (may be numbered).
111
Network layer
Stamps each packet with IP addresses of sender and the destination.
112
(Data) Link layer
Bottom layer used to physically send packet across the network.
113
Ethernet
Family of protocols for LAN data transmission.
114
Wi-Fi
Family of protocols for wireless data transmission
115
TCP
Transmission Control Protocol.
Transport Layer.
Segments data into numbered packets. Ensures all packets arrive and not corrupted.
116
UDP
User Datagram Protocol
Transport Layer.
Segments packets into numbered packets but doesn’t ensure all arrive or corrupted.
117
IP
Internet Protocol
Network Layer.
Stamps source and destination IP onto packets to route each packet correctly.
118
HTTP
HyperText Transfer Protocol
Application layer protocol for transferring
web pages.
119
HTTPS
HyperText Transfer Protocol Secure.
Application layer.
Protocol for transferring encrypted web pages.
120
FTP
File Transfer Protocol.
Application layer.
Protocol for transferring files.
121
SMTP
Simple Mail Transfer Protocol.
Application layer.
Protocol for sending emails.
122
IMAP
Internet Message Access Protocol
Application Layer.
Protocol for retrieving emails.
123
Security
Preventing unauthorised access to data. Also covers encryption.
124
Authentication
Requires user to provide credentials such as username or password.
125
Encryption
Taking plaintext and translating it into meaningless cipher-text. A key is required to decode. Used when transmitting sensitive information.
126
Firewall
Combines Hardware and Software. Inspects incoming packets and assesses their likelihood of being malicious.
127
MAC address
Media Access Control. Unique to every Network Interface Card. A network can use blacklisting or whitelisting to filter access.
128
Social Engineering
Manipulating people so that they give up confidential
| information.
129
Blagging (pretexting)
Creating an invented scenario engage a targeted victim.
130
Phishing
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
Pharming
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
Shouldering
Physically observing private information over their shoulder.
eg. PIN number
133
Malware / malicious code
Hostile or intrusive software
134
Computer Virus
Replicates itself and inserts code into other programs infecting the computer system.
Spread using social engineering or system vulnerabilities.
135
Reasons for creating a virus
Making Money eg. Ransomware
Political Statement
Curiosity or Vandalism
Sabotage or as a “zombie” in a DDoS attack.
136
Trojan
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
Spyware
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
Adware
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
Biometric Measures
```
Fingerprints
Face recognition
Iris scanning
Retina Scanning
Hand geometry
```
140
Password Systems
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
CAPTCHA
Distinguishes bots from people. Usually graphical puzzles which are simple for humans but difficult for programs without good AI.
142
Email Confirmation
2-step authentication. Uses secondary source of information to ensure their human and it’s a legitimate email.
143
Automatic Software Updates
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
Penetration Testing
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
White-box penetration testing
Crackers have insider knowledge of the system. Simulates a malicious insider.
146
Black-box penetration testing
No prior knowledge. Simulates malicious outsider.
147
Mobile Technologies
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
Wireless Technology
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
Theft of Computer Code
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
Algorithm Copyright
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
Cracking and Hacking
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
Wearable technology
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
Computer-based implant.
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.
