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computer science > Data > Flashcards

Data Flashcards

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1
Q

what is a character set?

A

a character set is a table that matches together a character and a binary value

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2
Q

what are the two common character sets?

A

ASCII and unicode

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3
Q

why are character sets necessary?

A

they allow computers to exchange data

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4
Q

Describe 3 differences between ASCII and unicode?

A

ASCII

  • uses binary
  • tiny set of characters
  • less memory required per character

Unicode

  • uses hexadecimal
  • large set of characters
  • more memory required per character
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5
Q

what does ASCII stand for?

A

American standard code for information interchange

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6
Q

how many different data types are there?

A

5

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7
Q

what is a character ?

give an example

A

a single character , such as a letter, number, punctuation or symbol

e.g. T 8 ?

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8
Q

what is a string?

give an example

A

a sequence of characters, including letters, numbers and punctuation

e.g. harry styles
14:50 pm
cinderella 2

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9
Q

what is an integer?

give an example

A

a whole number

e.g. 475
-84
10

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10
Q

what is a real?

give an example

A

a decimal number

  • 5.21
    0. 01345
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11
Q

what is a boolean?

give an example

A

an answer that only has two possible values

true/false
yes/no
0/1

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12
Q

what data type are telephone numbers stored as ?

A

string

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13
Q

what are the two main type of graphics used in a computer system?

A

raster (aka bitmap)

vector

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14
Q

describe 3 differences between raster(bitmap) and vector images
give examples

A

Raster

  • made up of a grid of pixels
  • if scaled to a larger size, image loses image quality
  • generally larger in size as data is stored for each pixel
    e. g. photographs and screenshots

Vector

  • use objects (lines and shapes) to mathematically form shapes
  • if scaled to a larger size, does not lose any image quality
  • generally smaller in file size
    e. g. logos and cartoons
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15
Q

formula to calculate file size

A

file size = resolution x colour depth

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16
Q

what is the colour depth/bit depth?

A

the number of bits that are used to represent each pixel’s colour

17
Q 
how many colours can be represented with a colour depth of 
1 bit 
2 bit 
3 bit 
5 bit 
1 byte 
?
A 
1 = 2 colours 
2 = 4 colours 
3 = 8 colours 
5 = 32 colours 
1 byte (8 bits) = 256 colours
18
Q

what is the RGB colour model?

A

the red green blue colour model uses 3 bytes (a byte of 256 red green and blue shades ) that together can represent 16.7 million different colours

19
Q

what is metadata?

give examples of image metadata

A

metadata is additional information about a file

e.g 
dimensions
colour depth 
make 
model
orientation 
exposure time
19
Q

what is metadata?

give examples of image metadata

A

metadata is additional information about a file

e.g 
dimensions
colour depth 
make 
model
orientation 
exposure time
20
Q

an image file has a width of 120 pixels , a height of 120 pixels and a colour depth of 1 . what is the file size in bytes

A

resolution is height x width
120 x 120 = 14400
colour depth = 1 bit

file size = resolution x colour depth
file size = 14400 x 1 = 14400

file size in bytes = 14400 / 8 = 1800 bytes

21
Q

how is an analogue sound wave converted to digital data (binary) ?

A

the sound is sampled using an ADC (analogue to digital convertor) and stored as a binary value called a sample

22
Q

what is a sample rate?

what is it measured in?

A
  • the number of samples taken per second

- measured in kilohertz (kHz)

23
Q

explain 2 ways an audio file will be affected if the sample rate is increased

A
  • the higher the sample rate the better the audio quality as the digital data more closely resembles an analogue wave
  • higher sample rates result in larger file sizes because more data is stored for each individual sample
24
Q

what is bit depth ?

A

the number of bits available to represent each sample

25
Q

explain 2 ways an audio file will be affected if the bit depth is increased

A
  • the higher the bit depth , the more bits are available to be used for each sample
  • therefore the quality is often higher as the wave more closely resembles an analogue wave
  • the file size will also be larger as each sample stores additional bits
26
Q

what is bit rate?

what is it measured in?

A

the amount of audio data processed per second

measured in kilobytes per second (kbps)

27
Q

an audio file has a bit depth of 8 , a sample rate of 10 and its 12 seconds long . What is the file size in bytes?

A 
bit rate = sample rate x bit depth 
8 x 10 = 80 
bit rate x no. seconds = file size 
80 x 12 = 960 bits 
to convert answer from bits to bytes dive by 8
960 /8 = 120 bytes
28
Q

describe 3 benefits of compressing a file

A
  • files take up less storage (so more files can be stored)
  • can be transferred quicker (as they are smaller )
  • files can be read from or written to quicker
29
Q

describe the differences between lossy and lossless compression

A

lossy compression

  • uses an algorithm to analyse a file and remove data that cannot be seen or heard by humans . e.g. frequencies (this reduces file size)
  • further lossy compression will remove data that humans can see/hear
  • removes data permanently so a file can never return to its original format
  • often used with images , audio and video to reduce the file size

lossless compression

  • reduces the size of a file without permanently removing any data
  • this means the file can return to its original format when decompressed so quality is not lost
  • larger file size as no data has permanently been removed
  • used with files that would not work if data was removed e.g. executable files or word documents
30
Q

a text file was 72KB and was compressed to 8KB. state the compression ratio

A

72/8 = 9:1

31
Q

a 20 MB file is compressed with the ratio of 5:2. what is the size of the compressed file?

A
32
Q

compression ratio formula

A

compression ratio = original file size / compressed file size

computer science (12 decks)

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