A Level AQA CS > Unit 3 - Data Representation > Flashcards

Unit 3 - Data Representation Flashcards

(82 cards)

Study These Flashcards
1
Q

What is a set?

A

A set is a well-defined collection of objects.
- Objects in the set are members or elements,
- A set is unordered,
- Each member in a set can only occur once,
- A set is usually denoted by a capital letter,
- A member is usually denoted by a lower case letter.
- A set can be defined by listing every member,
- A set can be defined by stating the properties held by the members, but not by the non-members,
- The members are enclosed by { } and separated by a comma.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

What is the set of natural numbers?

A

The set containing all positive integers greater than or equal to zero.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

What is the set of whole numbers?

A

The set containing all integers.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

What is the set of rational numbers?

A

The set containing all numbers which can be expressed as a fraction.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

What is the set of irrational numbers?

A

The set containing all numbers which cannot be expressed as a fraction.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

What is the set of real numbers?

A

The set containing all numbers which can be used as a measurement. Ultimately, the combination of the sets of rational and irrational numbers.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

What is the set of imaginary numbers?

A

The set of imaginary numbers consists of numbers that can be expressed as a real number multiplied by the imaginary unit (root(-1)).

In other words, all numbers not in the set of real numbers.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

What are ordinal numbers?

A

Numbers used to describe the position of values in a list or set.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

What is a number system?

A

A way of using symbols to represent values, such as the denary/decimal system, which uses the 10 characters 0-9.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

What is a base, in the context of number systems?

A

The amount of symbols that system uses to construct values.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

What is the denary/decimal number system?

A

The number system which represents numbers with 10 symbols, 0-9.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

What is the binary number system?

A

The number system which represents numbers with 2 symbols, 0 and 1.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

What is the hexadecimal number system?

A

The number system which represents numbers with 16 symbols, 0-F.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

Why is hexadecimal used to display binary values often?

A
  • Each hexadecimal character represents 4 binary characters, making it easier and quicker to read, write and remember,
  • It is very easy to convert to and from binary.
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

Why does every computer contain millions, if not billions of simple circuits containing only a switch?

A

This is because a switch can represent binary 1 and 0 (ON and OFF) very efficiently.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

What is a bit?

A

A single binary digit.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
17
Q

What is a byte?

A

A collection of 8 bits.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
18
Q

What are the decimal prefixes used for bytes by the public?

A
  • kB (Kilobyte) - 10^3 = 1,000
  • MB (Megabyte) - 10^6 = 1,000,000
  • GB (Gigabyte) - 10^9 = 1,000,000,000
  • TB (Terabyte) - 10^12 = 1,000,000,000,000
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
19
Q

What are the binary prefixes used for bytes by computer scientists and computers themselves?

A
  • KiB (Kibibyte) - 2^10 = 1,024
  • MiB (Mebibyte) - 2^20 = 1,048,576
  • GiB (Gibibyte) - 2^30 = 1,073,741,824
  • TiB (Tebibyte) - 2^40 = 1,099,511,627,776
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
20
Q

How does pressing a key on a keyboard lead to something happening on a computer?

A

Each key corresponds to a binary value which, when a key is pressed, gets sent to the computer, where the keyboard’s driver program translates this value into a format which is understood by the computer and the computer uses that value to do what it does when said key is pressed.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
21
Q

What is ASCII?

A

A standard for encoding keys on a keyboard as specific, consistent values. Originally used 7 bits, later 8 bits.

ASCII - American Standard Code for Information Interchange.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
22
Q

What is Unicode?

A

A standard for encoding keys on a keyboard as specific, consistent values, used to encode characters from every used language. Each character has a variable length of 16 or 32 bits.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
23
Q

What are transmission errors?

A

When data is transmitted, it doesn’t always arrive in the same format that it was sent because of various circumstances like:
- Electrical interference,
- Power surges,
- Synchronisation issues,
- Wear and tear on the cable or connectors.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
24
Q

What are the 4 error detection techniques on the course?

A
  • Parity bits,
  • Majority voting,
  • Check digits,
  • Checksums.
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
25
What is a parity bit?
A bit in each byte is dedicated to keeping the number of ones consistent in every byte. If a byte does not match the parity (either even or odd), then a transmission error affects the byte and the receiver requests for that byte to be resent.
26
What is majority voting?
An error detection technique where each bit is sent multiple times and the value which appears the most for that bit is used.
27
What is a check digit?
A check digit is an additional digit at the end of a string of other numbers designed to check for mistakes in input or transmission.
28
How does the Modulo 10 system work? (Error detection technique for ISBN codes).
For the 1st 12 digits, each even value is given a weight of 3 and each odd value is given a weight of 1. You then multiply each digit by its weight and add the results together. You divide this result by 10, and subtract the remainder of that from 10. The result of this process should be the 13th digit.
29
What is a checksum?
A checksum is a value sent with data which is the total sum of all bytes in the transmission. It is calculated using an algorithm. The receiving computer recalculates the checksum based on the data it received and compares it with the checksum received or a known, expected value. If it does not match, the data may have been altered or corrupted during transmission and the data is resent.
30
What are the rules of binary addition?
0 + 0 = 0 1 + 0 = 1 1 + 1 = 10 1 + 1 + 1 = 11
31
What is an oveflow error?
An overflow error occurs when the computer calculates something and attempts to store it in a location without enough space for the value.
32
What are the rules of binary multiplication?
0 * 0 = 0 0 * 1 = 0 1 * 0 = 0 1 * 1 = 1
33
What is two's complement?
A way of storing negative numbers in binary which works by storing the last bit of a value as a negative number and adding the values of every other bit onto it.
34
How to convert regular binary to two's complement?
Flip every bit and then add 1 to the resulting value. 00000001 (1) 11111111 (-1)
35
How to determine the range of binary numbers?
The range is from 0 to 2^(n-1) - 1, where n is the number of bits storing the number.
36
How to determine the range of two's complement binary numbers?
The range is from -(2(n-1)) to 2^(n-1) - 1, where n is the number of bits storing the number.
37
What are the rules of binary subtraction?
0 - 1 = -1 1 - 1 = 0 10 - 1 = 1 1 - 0 = 0 0 - 0 = 0
38
What are the rules of binary division?
0 / 0 = undefined 0 / 1 = 0 1 / 0 = undefined 1 / 1 = 1 10 / 1 = 1
39
How do binary fractions work?
Bits after the binary point become 2^-n rather than 2^(n-1) for those before it. n is the distance from the point.
40
How does fixed-point binary function?
A fixed-point binary value uses a specified number of bits where the placement of the binary point is fixed.
41
What is digital data?
Data stored in a computer (discrete).
42
What is analogue data?
Data in the world (continuous).
43
How do humans see?
Light wave are reflected off objects, which gives them a specific frequency (which determines their colour). When these waves enter the human eye, they are detected by the retina in the back of the eye, and this information is sent to the brain, and it creates an "image" from all the wave that have been detected in a specific interval.
44
How do cameras capture images?
They detect light waves in a certain interval, split up the detected light into pixels on a grid and estimates the colour of all the light waves in each specific pixel, forming the result into an image.
45
What are Bitmap/Raster graphics?
Digital images stored using a grid of pixels, which have a range of possible colours.
46
What are common bitmap files?
BMP JPG GIF PNG TIFF
47
What is the resolution of a bitmap file?
The number of pixels used to make up a bitmap image, defined by width * height. A larger number leads to higher image quality but also larger file size.
48
What is the relationship between resolution and image size.
Resolution does not determine the image size. If an image is made bigger (or smaller), the size of each pixel grows or shrinks to maintain the required resolution. This is why there is a deterioration in quality when a bitmap is resized.
49
What is the colour depth of a bitmap file?
The finite number of colours that a pixel could possibly be, defined by a number of bits. A higher colour depth gives a greater range of colour and a better quality of image, though increasing file size.
50
How do you calculate file size of bitmap images?
number of pixels * colour depth + metadata = file size
51
What is metadata?
Metadata is data about data and is stored in the same file as the data itself.
52
What are vector graphics?
Vector images are made up of geometric shapes or objects, stored through mathematic equations, rather than by manipulating individual pixels.
53
What is an ADC?
An analogue to digital converter.
54
What is a DAC?
A digital to analogue converter.
55
How do we hear sound?
Sound is a result of changes in air pressure due to waves, these pressure fluctuations cause our eardrums to vibrate and these vibrations are interpreted by nerves in our ears as sound.
56
What are some ADCs and DACs?
An example of an ADC is a microphone or a camera. An example of a DAC is a speaker or a monitor.
57
How do ADCs work with sound?
When a sound wave hits an ADC, an amplifier in it records the changes and quantises them to measure wave height (amplitude). this value becomes an integer which gets stored as a digital value.
58
What is the sampling rate of sound files?
The amount of samples of the wave taken in a single second. Each sample happens at a regular period. The higher the sampling rate, the higher the quality and storage demand.
59
What is the sampling resolution of sound files?
The range of values that the amplitude can be for each sample. This is specifically the amount of bits used to store the amplitude in each sample. The higher the sampling resolution, the higher the quality and storage demand.
60
How do you calculate the file size of a sound file?
Sample rate * resolution * length in seconds + metadata = file size
61
What are some characteristics of sound in the real world?
- Made up of numerous sound waves at various frequencies - Continuous
62
Why is there a limit to the lowest sampling rate that can accurately record a sound?
This is because sounds are made up of multiple components with different frequencies and so if you sample at a rate too low, you may only capture some of the sound waves, as some may have a frequency so high that you miss out repetitions of the wave.
63
What is Nyquist Theorem?
The idea that the limit on the sampling rate must be at the very lowest twice the frequency of the most frequent sound wave in a sound in order to accurately capture it.
64
What is the range of frequencies the human ear can hear?
20Hz to 22kHz (22,000Hz)
65
What is MIDI?
The MIDI standard (Musical Instrument Digital Interface) is a standard for sound synthesis.
66
What is a benefit of using MIDI rather than sending recorded sound files over?
- This significantly reduces the amount of data that needs to be transferred.
67
What is a detriment of using MIDI rather than sending recorded sound files over?
Synthesised sound may be less realistic than recorded instruments.
68
What are event messages?
Messages sent to devices that are linked to a sound processor which helps them synchronise their sound output. Some examples include: - Synchronising tempo, - Controlling pitch, - Changing volume, - Introducing and silencing other instruments in a digital orchestra
69
What is compression?
The reduction in size of files on a computer.
70
Why is compression useful?
- Storage space is limited and so reducing demand is good, - Smaller files transfer quicker, - Buffering on audio and video streams is less likely to occur, - Less bandwidth is used, allowing you to transfer more files with the same amount of bandwidth,
71
What is lossy compression?
Lossy data compression is where non-essential data is permanently removed, for example nearly identical shades of the same colour in an image or frequencies in sound files that lie beyond human hearing.
72
What is lossless compression?
Lossless data compression is where all data in a file is retained while making it smaller. Typically done by spotting and summarising patterns in data.
73
How does JPG compression work?
Pixels with very similar colour values are simplified into having the same value.
74
How does MP3 compression work?
Sounds in frequency ranges we cannot hear and those which do not make a substantial impact on the sound overall are removed.
75
How does Run Length Encoding work?
Run Length Encoding is a form of lossless compression that summarises consecutive patterns of the same data.
76
How does dictionary compression work?
Spots regularly occurring data and stores it separately in a dictionary and the reference to the entry in the dictionary is stored in the main file thereby reducing the original data stored. Even though the dictionary produces additional overheads the space saving negates this problem in the majority of cases.
77
What is encryption?
Encryption is a way of making sure data cannot be understood if you don’t possess the means to decrypt it.
78
How does encryption work?
Plaintext of a message sent is encrypted using a cipher algorithm and key into equivalent ciphertext, when received, the ciphertext is decrypted back to plaintext using the same or a different key.
79
What is the Caesar cipher?
A form of encryption where letters in the alphabet are shifted by a consistent amount.
80
What is a brute force attack?
A brute force attack is a cyberattack method where attackers use trial and error to guess passwords, login credentials, or encryption keys until they gain unauthorized access.
81
What is frequency analysis?
Frequency analysis is a method of defeating the Caesar cipher which uses the fact that letters are not used equally often to determine common patterns which can allow you to find common words and thus begin decrypting the ciphertext.
82
What is the Vernam cipher?
The only form of encryption which is truly unbreakable. It uses a truly random encryption key that is at least equal in length or longer than the ciphertext, which is delivered independently of the message and is destroyed immediately after use. Encryption and decryption of the message is performed bit by bit using an exclusive or (XOR) operation with the shared key.
A Level AQA CS
flashcards
Decks in class (13)
# Cards
Brainscape helps you reach your goals faster, through stronger study habits.
© 2026 Bold Learning Solutions. Terms and Conditions