Computer Science: Key Knowledge Flashcards
1
Q
What is volatile memory?
A
Memory which will lose all the data when the power is turned off
2
Q
Is RAM volatile or non-volatile?
A
Volatile
3
Q
What is fast access storage?
A
Storage which is quicker to access by the CPU
4
Q
What does RAM hold?
A
Parts of the operating system currently in use when the PC is in use
5
Q
What are the 5 data types?
A
Integer, real/float, char, string, Boolean
6
Q
How large is RAM?
A
A few GB in size
7
Q
Are CPU registers and CPU cache volatile or non-volatile?
A
Volatile
8
Q
What is an integer?
A
A while number such a 156, 0 or -54
9
Q
How much space does an integer type take up?
A
2 bytes
10
Q
What is a float or real number?
A
Number with a fractional part such as 1.5276, -68.4 or 20.0
11
Q
How much space does a float or real number take up?
A
4 bytes
12
Q
What is a char date type?
A
A single ASCII character such as A, b, 3, ! or space
13
Q
How much space does a char data type take up?
A
1 byte
14
Q
What is a string?
A
Data containing zero or more characters
15
Q
How much space does a string take up?
A
1 byte per checker in the string
16
Q
What is a Boolean?
A
Can only take the values true/false
17
Q
How much space does a Boolean take up?
A
Theoretically just 1 bit, but in high level languages, more like a byte
18
Q
What is virtual memory?
A
Volatile memory created temporarily on the storage drive
19
Q
When is virtual memory required?
A
When the computer is running too many processes/RAM is being slow
20
Q
How does virtual memory affect the computers speed?
A
It slows the computer down - copying to hard disk takes much longer than reading/writing RAM
21
Q
What is a syntax error?
A
The rules for writing python have been broken
22
Q
What is a logic error?
A
The code runs but gives an incorrect answer
23
Q
What is concatenation?
A
Joining together. The ‘+’ concatenate operator is used to join together strings
24
Q
Is ROM volatile or non-volatile memory?
A
Non-volatile
25
What is non-volatile memory?
When the data is stored even when the power is turned off
26
What is ROM used for?
Launching a PC’s operating system from the BIOS. Also used in embedded systems as a small store of software
27
What is the CPU?
The computer’s brain.
28
What is the purpose of the CPU?
Carry out the fetch-decode-execute
29
What is the fetch-decode-execute cycle?
CPU fetches next instruction from RAM, works out what to do and then carries out the instruction
30
What is the purpose of the Control Unit (CU)?
Controls the flow of data inside the CPU (to registers) and outside the CPU. to RAM and input/output devices
31
Is the hard disk volatile or non-volatile?
Non-volatile
32
How does sample rate frequency affect accuracy and sound file size?
The greater the sample frequency, the greater the accuracy and file size
33
What is the equation for calculating sound file size?
Sound file size = sample rate x bit depth x duration
34
How far do hex conversions go up to?
15
35
What is the largest hex number?
F
36
What is the largest binary number?
1111
37
What sound range can humans hear?
20 - 20,000 Hz
38
What are analogue signals?
Continuous
39
What are digital signals?
Discrete
40
How is sound digitized?
By repeatedly measuring and recording the sound wave
41
What does ADC stand for?
Analogue to digital conversions (inputs to digital signals)
42
What does DAC stand for?
Digital to audio converter (digital signals to outputs)
43
What is a sound sample?
A measurement of the amplitude of a sound wave at a given time
44
What determines how closely a wave is sampled on the y-axis?
Bit depth
45
What is the sample rate?
Samples per second (measured in Hz)
46
What is sample resolution?
The number of bits used to record each measurement
47
What does 1Hz mean?
1 sample per second
48
What is metadata?
Data about data
49
Give 2 examples of metadata:
Any 2 from:
file size, author, name, date last opened, etc.
50
What does DPI stand for?
Dots Per Inch
51
How does DPI affect image quality?
Higher DPI, better image quality
52
What are images made up of?
Pixels
53
What does each pixel represent?
A colour that is given a unique binary code
54
What is resolution?
The number of pixels in an image.
55
How does resolution effect image quality?
Higher resolution, better image quality
56
How does resolution affect file size?
Higher resolution, higher file size
57
What is increased colour depth?
Where more bits are stored per pixel - better quality, larger file size
58
Explain how to calculate the file size of a bitmap:
1. Find the number of pixels. Example - 16 x 16 = 256
2. Count the colours. Check powers. Example - 7 colours. 2^3 = 8 (2^2 is not enough)
3. So we need 3 bits per pixel
4. Size of an image = no. of pixels x bit depth -> 768 bits
5. If necessary, divide by 8 to convert to bytes
59
What is any number to the power of 1 equal to?
0
60
Why do we use binary?
Because the CPU is made up of millions of transistors. These can either be on/off - 0/1.
61
What is MOD?
The remainder after dividing.
62
What is 5 MOD 2?
1
63
What are denary numbers?
Normal numbers - base 10
64
What is lossless compression?
Compression where no data is lost
65
What is lossless compression?
Compression where some data is lost (not really a visible difference, but decreased quality)
66
How does image quality affect file size?
Higher file size, better image quality. Lower file size, lower quality.
67
What is capacity?
How much something can store
68
What is portability?
How portable something is
69
What is durability?
How durable something is
70
What is speed (of data transfer)?
How fast data is transferrd
71
What is reliability?
How reliable something is, how long it will last
72
What is price?
How much something costs
73
Give 2 examples of input devices:
Any 2 from:
Mouse, keyboard, joystick, barcode scanner, microphone
74
Give 2 examples of output devices:
Any 2 from:
Headphones, speakers
75
What is the equation for calculating text file size?
Text file size = Bits per character x Number of characters
76
What are the 3 types of secondary storage?
Optical, magnetic, solid state
77
Name 2 examples of solid state storage:
Any 2 from:
USB flash drive, SSD hard drive, SD card
78
Name 2 examples of optical storage:
Any 2 from:
Blu-ray, DVD RAM, CD ROM
79
Name 2 examples of magnetic storage:
Any 2 from:
Hard disk drive, Floppy disk drive, Backup tape drive
80
What does magnetic storage consist of?
This consists of tiny magnetic particles responsible for storing your data
81
What does optical storage consist of?
This consists of a laser beam which burns dark pits onto the surface of a disk. The pits are read in binary - a pit represents a '1', no pit represents a '0'
82
What does solid state storage consist of?
This consists of a series of electronic switches which hold data temporarily. Open switches represent a '1'. Closed switches represent a '0'. These are read in binary.
83
What does != mean?
Not equal to
84
What does > mean?
Greater than
85
What does < mean?
Less than
86
What does >= mean?
Greater than or equal to
87
What does <= mean?
Less than or equal to
88
What does == mean?
Equal to
89
What does the hat '^' symbol mean?
To the power of
90
What does the '*' symbol mean?
Multiply
91
What does the '/' symbol mean?
Divide
92
What does ASCII use to represent characters?
Bits
93
How many values does ASCII represent?
128 (0-127)
94
What is Null in ASCII?
00000000
95
What is A in ASCII?
10000001
96
What is DEL in ASCII?
11111111
97
What is the equation for sound file size?
File size (bits) = sample rate x bit depth x duration
98
Give one advantage and one disadvantage of optical secondary storage:
Advantage: Relatively low cost
Disadvantage: Low durability - risk of scratching disk
99
Give one advantage and one disadvantage of solid state secondary storage:
Advantage: Very portable
Disadvantage: Expensive
100
Give one advantage and one disadvantage of magnetic secondary storage:
Advantage: Largest capacity
Disadvantage: Low durability - moving parts
101
Name the different types of sorts:
Binary search, bubble sort, merge sort, linear search, insertion sort
102
Give 2 examples of issues:
Any 2 from:
Ethical, cultural, environmental, technological, industrial
103
What is selection?
An if statement. Something which runs depending on a specific condition
104
What is iteration?
A loop. A piece of code that is repeated.
105
What are the 8 conditions laid out in the Data Protection Act? (JUST READ IF NECESSARY)
1. Confidential information that is no longer required should be properly disposed of
2. Data must be obtained fairly - not transferred company to company
3. Data collected for one purpose (ie. CCTV) cannot be used for another purpose (ie. spying on staff)
4. Do not disclose/reveal data without a person's consent
5. Data must be relevant and not excessive
6. Data must be accurate and up to date
7. Retain data for no longer than necessary
8. Provide a copy of the data upon request
106
What are the 4 offences listed in the Computer Misuse Act?
1. Unauthorised access to computer material
2. Unauthorised access with intent to commit or facilitate a crime
3. Unauthorised modification of software or data
4. Making, supplying or obtaining anything which can be used in computer misuse offences
107
What are inventions covered by?
Patents
108
What do patents do?
Prevent anyone using an idea for 20 years
109
What are books, music and software covered by?
Copyright
110
How long does copyright last?
70 years after publication or the author's death
111
What is the purpose of copyright?
To allow the author to decide how their work can be used
112
What is open source software?
Software where the source code is made available. Users may legally modify the source code and share it under the same licence
113
What is proprietary software?
Software where only the compiled code is released and usually this costs money. The licence prevents users from modifying or editing the software. Examples include word and excel.
114
What does APPEARS stand for?
A - Accurate
P - Purpose
P - Processing
E - Excessive
A - Accountable
R - Retention
S - Security
115
How many values are in Extended ASCII?
256
116
How many bits does Extended ASCII use?
8
117
How many bits does ASCII use?
7
118
How many values are in Unicode?
65, 536
119
How manty bits does Unicode use?
16
120
What does ASCII stand for?
American Standard Code for Information Interchange
121
How manty bits does Unicode use?
16
122
How does lossless compression work?
Algorithm finds groups of repeating data and records the data once along with the number of repetitions
123
Give 2 examples of network security threats:
Any 2 from:
Poor network policies, malware, phishing, SQL injection, DoS attack, data interception, brute force attacks, social engineering
124
What is social engineering?
A technique used by criminals to trick/manipulate people into revealing confidential information - info is gained to gain computer access
125
Give 2 examples of social engineering:
Any 2 from:
Fake emails which require info/downloads, USB in a public zone, phishing
126
What is phishing?
Sending emails from trusted organisations (ie. tax, bank) to trick someone into providing account information
127
What is a brute force attack?
Where software is used to try every possible combination of words, numbers and symbols to crack a password
128
How could you prevent a brute force attack?
Limit number of password attempts, use captchas (swirly letters computers can't read)
129
What is a Denial of Service attack?
A criminal uses software to bombard a web server with fake requests from one computer/internet connection. This uses up server memory and CPU cycles in order to crash the server - more often for revenge than obtaining data
130
What is a Distributed Denial of Service attack?
A DoS attack which uses many computers infected with botnet malware to spam servers with simultaneous requests
131
What is data interception?
Where someone gets in between you and what you're doing online - if connected to a risky network, they may spy on your screen and even edit messages sent from your device
132
Give 2 ways in which data interception could be prevented:
Any 2 from:
VPN, up to date anti-viral software, being alert to phishing scams, spotting the signs of a 'man in the middle' - long sudden page delays, HTTPS to HTTP in the URLs
133
What does VPN stand for?
Virtual Private Network
134
What are the 4 types of harmful software?
Malware, Spyware, Ransomware, Trojans (as in trojan horse)
135
What is SQL Injection?
When an attacker enters malicious code into a web forum. If there are any vulnerabilities, the injection can bypass the authentication process allowing access to the backend database
136
Give 2 ways to prevent SQL injection:
Any 2 from:
Updating and patching software regularly, using a firewall to filter data, using data validation to check input data (ie. email format '@')
137
What are network policies?
Formal documents containing the rules that you must follow in order to use a network
138
What is an embedded system?
A computer system that is made up of both hardware and software - often known as firmware
139
Give 2 examples of embedded systems:
Any 2 from:
MRI scanner, watch, traffic lights, microwave, dishwasher
140
What does CPU stand for?
Central Processing Unit
141
Order the levels of cache by speed (1 being fastest):
Level 1, Level 2, Level 3
142
What is the function of the Control Unit (CU)?
Decodes instructions and controls the timing of operations in the CPU
143
What is the function of the Arithmetic Logic Unit (ALU)?
Performs arithmetic and logic calculations
144
What is the function of the Program Counter (PC)?
Calls the next instruction
145
What is the function of the Memory Address Register (MAR)?
For the memory location of data to be fetched
146
What is the function of the Memory Data Register (MDR)?
Data recieved from the RAM
147
What is the function of the Accumulator (ACC)?
Stores the results from the ALU
148
What is clock speed?
Cycles per second, measured in Hz (Hertz)
149
How does clock speed affect CPU performance?
Faster the clock speed, faster the CPU can process instructions
150
What are processor cores?
The number of processor cores in one CPU. A dual-core processor has 2 processes in 1 integrated circuit, in order to perform 2 tasks at once
151
How will having more processor cores affect CPU performance?
More processor cores, faster CPU performance
152
What is cache?
Memory on the CPU that is faster than RAM but slower than registers
153
What are the rules when adding binary?
0 + 0 = 0
1 + 0 = 0
1 + 1 = 0 carry the 1
1 + 1 + 1 = 1 carry the 1
