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AS Computing - OW > 3.5 > Flashcards

3.5 Flashcards

(63 cards)

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1
Q

What is a natural number? (N)

A

is a whole number that is used in counting (0,1,2,3,4,5,6,7,8,9)

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2
Q

What is a rational number? (Q)

A

any value that can be expressed as a ratio or a fraction. Includes integer values e.g. 3/1, 6.74/1000

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3
Q

What is an irrational number? (Q’)

A

a value that cannot be expressed as a fraction and has an endless series of non-repeating digits. e.g. pi - 3.1415

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4
Q

What is an integer number? (Z)

A

a whole number that could be positive or negative e.g. -2,-1,0,1,2

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5
Q

What is a real number? (R)

A

any number that is natural, rational or irrational. The set of real numbers is the set of all possible real-world quantities.

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6
Q

What is an ordinal number?

A

to describe the numerical position of the object e.g. 1st, 2nd, 3rd

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7
Q

What are natural and real numbers for?

A

natural numbers - for counting

real numbers - for measurement

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8
Q

How do you find the number of bits in binary?

A

2^{n-1}

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9
Q

How many bits in 1 byte

A

8 bits

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10
Q

Fill the gaps

nibble, ____, byte, __, MB, __, TB, __

A

Nibble, bite, byte KB, MB, GB, TB, PB

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11
Q

What does ASCII stand for?

A

American Standard Code for Information Interchange

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12
Q

Computers use Two’s complement to represent what two numbers?

A

Positive & negative numbers

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13
Q

What is fixed point binary?

A

There is a fixed number of digits after the decimal point

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14
Q

What is fixed point binary used for?

A

For displaying decimal numbers (this makes the number more exact)

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15
Q

One advantage of fixed point binary?

A

it stores the number accurately

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16
Q

One negative of fixed point binary?

A

Cannot represent wide range of numbers in the same number of bits e.g. 4000 or 0.0001

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17
Q

What is the difference between signed and unsigned binary?

A

Signed binary means that the item can hold positive or negative values. Unsigned binary doesn’t distinguish between positive and negative values.

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18
Q

In unsigned binary, what is the minimum & maximum value for a given number of bits (n)?

A

2^{n-1} & 0

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19
Q

What is Ascii & Unicode?

A

Ascii uses an 8-bit encoding while Unicode uses a variable bit encoding.
Unicode is standardized while ASCII isn’t.
Unicode represents most written languages in the world while ASCII does not.

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20
Q

Why is error checking used?

A

because bits can change during transmission because of interference

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21
Q

What are the 3 forms of error checking & correction?

A
  • Parity bits
  • Majority voting
  • Check digits
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22
Q

What is parity bits?

A

a bit which acts as a check on a set of binary values, calculated in such a way that the number of 1s in the set plus the parity bit should always be even (or occasionally, should always be odd).

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23
Q

What is majority voting?

A

it selects put error & takes the majority to correct the error
data = 1011
transmission = 111 000 111 111
received = 101 001 110 111

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24
Q

What is Metadata?

A

‘data about data’

e.g. file name, date created, resolution, colour depth, creator

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25
What are the two forms sound is stored in?
Analogue = infinite amount of binary Digital = binary which computers understand
26
How do we convert analogue to digital?
We use a ADC (analogue to digital converter)
27
What is the ADC process?
Sound waves --> electrical voltage --> binary data
28
How do we convert digital to analogue?
We use a DAC (digital to analogue converter)
29
What is the DAC process?
binary data --> electrical voltage --> sound waves
30
If you have a higher sampling rate you get better _______
quality
31
What is resolution?
the number of pixels in the image
32
What is colour depth?
each pixel has a binary value assigned to it | the more bits assigned to each pixel the greater the number of colours that can be represented
33
Equation for file size(image)?
Resolution * colour depth OR width in pixels * height in pixels * colour depth
34
What is a stereo?
sound is often recorded for 2 channels. Left & right speakers can output very different sounds
35
How many channels in mono sound? How many channels in stereo sound? How many channels in a cinema?
1 channel 2 channels 5-6 channels
36
What is a bitmap image?
an image comprised of many pixels | each pixel is given a set binary value to represent a single colour
37
What is a pixel?
The smallest identifiable area of an image
38
What sample resolution do CD's have?
16 bit sample resolution
39
What is bit rate?
The number of bits per sound of size
40
Equation for file size(sound)?
bit rate * time (length of sound)
41
What is Nyquist's theorem?
The sample rate must be greater than twice the highest frequency component of interest in the measured signal
42
Why do we use compression on our files?
So we can send them quicker because they are smaller and take less time to send
43
What is lossless data compression?
No data is lost in compression & original can be restored exactly
44
What is lossy compression?
Data which is deemed non-essential is deleted(it can't be recovered)
45
What is Run length encoding (RLE)?
Is a form of lossless data compression in which runs of data (sequences in which the same data value occurs in many consecutive data elements) are stored as a single data value and count, rather than as the original run.
46
What is encryption?
is the conversion of data into a form that is difficult to read by an unauthorised third party
47
What is decryption?
Is the process of turning scrambled data into data that can be understood
48
What is cipher?
The algorithm for encryption
49
What is a key?
the secret information used to encrypt/decrypt the data
50
What is plaintext?
the original form of the data
51
What is ciphertext?
the encrypted data
52
What two ways can you use Caesar cipher?
Shift & keyword
53
How does Caesar cipher work?
You shift the alphabet a few places left or right OR Use a keyword to put in place and then put the alphabet after it
54
What is Vernam cipher?
It uses Baudot code & the XOR operator | Use a one-time pad key (randomly generated and change after 1 use)
55
What is computational security?
a cipher that is computationally secure is theoretically breakable but not when using current technology in a timeframe that would be useful
56
If the data is more important, would the encryption be of a higher or lower level?
Higher level of encryption for the best security
57
How does Vernam cipher work?
You turn the plaintext into ascii and then get the one time pad key and turn that into ascii, you then use XOR so make the encryption
58
Why is Caesar cipher so weak?
because as soon as you have worked out the key then all messages can be decrypted
59
Why is Vernam cipher completely secure?
Because if every letter is random then there is no pattern which makes it impossible to break computationally
60
What is MIDI?
It is a protocol designed for recording and playing back music on digital synthesizers that are supported by many makes of personal computer sound cards
61
What are the advantages of MIDI?
include small file size ease of modification & manipulation a wide choice of electronic instruments & synthesizer or digitally-sampled sounds.
62
How does symmetric encryption work?
one key is shared between the sender & receiver the key can be 128 bits or 265 bits billion of permutations
63
How does asymmetric encryption work?
use two keys in combination almost impossible to work out around 1024 bit keys both sender & receiver have their own public & private keys sender encrypts using recipients public key the recipient decrypts with their private key

AS Computing - OW (9 decks)

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