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CS > Data Representation 2 > Flashcards

Data Representation 2 Flashcards

1
Q

Order of Memory

A

bits
bytes
kilobytes
megabytes
mebibytes

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2
Q

How to Calculate the number of bits required for a given number of permeations?

A

Log2(permiations)

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3
Q

HEXADECIMAL

A

A - 1010 - 10
F - 1111 - 15

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4
Q

What’s the difference between a kilobyte and a kibibyte?

A

kilobyte is base 10 - 1000 bytes
kibibytes is base 2 - 1024 bytes

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5
Q

What is AND-ing?

A

To go from lower to uppercase in ASCII

Difference between lower and upper is 32.

Use the mask 1011111.

e.g. t=116

1110100
1011111
1010100

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6
Q

What is XOR-ing?

A

Still converting lower to upper (but also vice versa).

Only outputs true when inputs differ.

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7
Q

Which is better: ANDing or XORing and why?

A

XOR-ing is better because it can go both ways as opposed to AND-ing which only goes from lower to upper.

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8
Q

What is ASCII?

A

Stands for American Standard Code for Information Interchange.

Numerical representation of characters so computers can understand and use.

All characters are represented with a 7-bit binary

therefore: 2^7 = 128 characters

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9
Q

What are the flaws of ASCII?

A

128 characters is not enough to represent all possible characters, numbers and symbols.

Initially developed in English, and therefore does not represent all the other languages and scripts.

Widespread use of the web makes it more important to have a universal coding system.

Range of platforms and programs has increased with more developers around the world using a wide range

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10
Q

What is Unicode?

A

Follows the same basic principles as ASCII but uses more bits: can be 16 or 32 bits.

Includes international characters for over 20 countries and even includes conversions of classical and ancient characters.

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11
Q

State one difference between Unicode and ASCII?

A

Unicode uses more bits than ASCII.
16 or 32 bit.

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12
Q

What is a Parity Bit?

A

Method of defecting errors in data during transmission.

Count the number of 1’s in each byte before sending to see whether it is odd or even. At the receiving end, the code can be checked to see whether it is still odd/even.

even parity: need even amount of 1’s
odd parity: need odd amount of 1’s

Can detect the error but not correct it.

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13
Q

What is Majority Voting?

A

Each bit is sent three times (or any odd amount so long as you can achieve a majority vote)

Fixes error by choosing majority bit.

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14
Q

What is a Checksum?

A

Checksum is a calculated value sent alongside a block of data for error detection.

Checksum recalculated when packet is received.

If checksum received in packet matches recalculated checksum, days received correctly. If not: data corrupted.

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15
Q

What’s the difference between Analogue and Digital signals?

A

Analogue data is data that is infinitely variable and represented in a wave.

Alternatively, digital data is often represented as discrete values on and offs shown as set peak and troughs.

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16
Q

What is a Pixel?

A

A Pixel is a picture element.

The smallest addressable image of a picture.

17
Q

What is Colour Depth?

A

Number of bits stored for each pixel.

e.g. to make 2 colours you do 2^1 = 2, Colour Depth = 1

18
Q

How do you calculate Storage?

A

Size in Pixels (Resolution) x Colour Depth

19
Q

Bit Conversions

A

bits -> bytes (/8)
bytes -> kilobytes (/1000)
kilobytes-> MB (/1000)

20
Q

What are Vector Graphics?

A

Created using objects and coordinates.

An image made up of shapes.

X: Can’t create detailed images - too complex

✔️: Smaller files size.
Ability to scale up and down without distortion.

21
Q

What are Bitmap Graphics?

A

A calculation of pixels from an image mapped to specific memory location holding their binary colour value.

22
Q

Vector vs. Bitmap

A

VECTOR images scale without file size increase/decrease.

BITMAP images scale resulting in file size increase/decrease.

VECTOR images scale without distortion to image.

BITMAP distorts when scaled.

BITMAPs are better for photo editing.

BITMAPs require less processing power to display.

23
Q

What is Nyquist’s Theorem?

A

Sample at a frequency (at least) twice the rate; of the highest frequency (that can be present in the original signal).

Get a closer representation of the sound as one sample can lose data.

24
Q

What is MIDI?

A

Musical Instrument Digital Inteference.

Does not record analogue sound but recreate sound digitally.

Produces smaller files without loss of quality.

Allows for easy editing after recording.

No interference.

Struggles to recreate sounds made by traditional instruments.

Struggles to recreate human voice.

25
Q

What is Lossless Compression?

A

Compression does not lose any accuracy and can be decompressed into an identical copy of the original data.

e.g. zip files, WAV.

26
Q

What is Lossy Compression?

A

Results in lost detail/qualities from the original version.

Removes information from the original so the original cannot be recreated.

Loses file accuracy, smaller than lossless compression.

27
Q

What is RLE (run length encoding)?

A

Looks for repeated patterns in the file and instead of recording each pattern separately, it stores information on how many times the pattern occurs in a row.

e.g. 6W3B

28
Q

What is an Edge-Triggered D-type Flip Flop?

A

A logic circuit which can be used ad a memory unit for storing the value of a single bit.

Two inputs, one for data, one for a clock signal.

One output, holds the value of the stored bit.

29
Q

What is a Half Adder?

A

A, B. And gate + XOR gate on top

30
Q

What is Full Adder?

A

A, B XOR
A, B AND
ABxor, C XOR
abxor, C AND
abxorcand, aband, OR

31
Q

What is Encryption?

A

The process of turning plaintext (text you can read) into scrambled ciphertext, which can only be understood if it is decrypted.

32
Q

What is Decryption?

A

The process of deciphering encrypted data or messages.

Ciphertext to plaintext usually using a key.

33
Q

What precautions are necessary to ensure the Vernan Cipher stays secure?

A

• only two copies of the key-tape
• sender and receiver have the same key
• key-tape is only used once. if intercepted, frequency analysis could be used to identify patterns
• key-tape is destroyed immediately after
• equipment is TEMPEST proof (cannot be spied on)
• key tape was not compromised during transpirt

CS (12 decks)

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