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Computer science GCSE > Chapter 1: Data Representation > Flashcards

Chapter 1: Data Representation Flashcards

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1
Q

Definition of bit

A

the basic computing element that is either 0 or 1, an is formed from the words Binary digit (Bit)

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2
Q

Definition of binary number system

A

a number system based on 2 and can only use the values 0 and 1

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3
Q

Definition of hexadecimal number system

A

a number system based on the value 16 which uses denary digits 0 to 9 and letters A to F

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4
Q

Definition of error code

A

an error message generated by the computer

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5
Q

Definition of MAC address

A

standing for Media Access Control, this address (given in hexadecimal) uniquely identifies a device on the internet; it takes the form: NN-NN-NN-DD-DD-DD, where NN-NN-NN is the manufacturer code and DD-DD-DD is the device code NN-NN-NN-DD-DD-DD

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6
Q

Definition of IP address

A

Internet Protocol identified either as IPv4 or IPv6; it gives a unique address to each device connected to a network identifying their location

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7
Q

Definition of HTML

A

HyperText Mark-up Language is used in the design of web pages and to write, for example, http(s) protocols; in the context of this chapter, colours used in web pages are assigned a hexadecimal code based on red, green and blue colours

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8
Q

Definition of overflow error

A

the result of carrying out a calculation that produces a value that is too large for the computer’s allocated word size (8-bit, 16-bit, 32-bit, and so on)

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9
Q

Definition of logical shift

A

an operation that shifts bits to the left or right in a register; any bits shifted out of a register (left or right) are replaced with zeroes

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10
Q

Definition of two’s complement

A

a method of representing negative numbers in binary; when applied to an 8-bit system, the left-most bit (most significant bit) is given the value -128

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11
Q

Definition of ASCII code

A

a character set for all the characters on a standard keyboard and control codes

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12
Q

Definition of character set

A

a list of characters that have been defined by computer hardware and software. The character set is necessary so that the computer can understand human characters

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13
Q

Definition of Unicode

A

a character set which represents all the languages of the world (the first 128 characters are the same as ASCII code)

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14
Q

Definition of sampling resolution

A

the number of bits used to represent sound amplitude in digital sound recording (also known as bit depth)

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15
Q

Definition of bit depth

A

the number of bits used to represent the smallest unit in a sound file

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16
Q

Definition of colour depth

A

the number of bits used to represent the colours of a pixel

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17
Q

Definition of sampling rate

A

the number of sound samples taken per second in digital sound recording

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18
Q

Definition of bitmap image

A

an image made up of pixels

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19
Q

Definition of pixel

A

derived from the term ‘picture element’, this is the smallest element used to make up an image on a display

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20
Q

Definition of image resolution

A

the number of pixels in the X-Y direction of an image, for example, 4096 x 3192 pixels

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21
Q

Definition of pixelated (image)

A

this is the result of zooming into a bitmap image; on zooming out the pixel density can be diminished to such a degree that the actual pixels themselves can be seen

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22
Q

Definition of pixel density

A

number of pixels per square inch

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23
Q

Definition of compression

A

reduction of the size of a file by removing repeated or redundant pieces of data; this can be lossy or lossless

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24
Q

Definition of bandwidth

A

The maximum rate of transfer of data across a network, measured in kilobits per second (kbps) or megabits per second (Mbps)

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25
Q

Definition of lossy (file compression)

A

a file compression method in which parts of the original file canot be recovered during the decompression process, for example, JPEG, mp3

26
Q

Definition of lossless (file compression)

A

a file compression method that allows the original file to be fully restored during the decompression process, for example, run length encoding (RLE)

27
Q

Definition of audio compression

A

a method used to reduce the size of a sound file using perceptual music shaping

28
Q

Definition of MP3

A

a lossy file compression method used for music files

29
Q

Definition of MP4

A

a lossy file compression method used for multimedia files

30
Q

Definition of JPEG

A

from Joint Photographic Expert Group; a form of lossy file compression used with image files which relies on the inability of the human eye to distinguish certain colour changes and hues

31
Q

Definition of run length encoding (RLE)

A

a lossless file compression technique used to reduce the size of text and photo files in particular

32
Q

Error codes

A

Error codes are often shown as hexadecimal values. These numbers refer to the memory location of the error and are usually automatically generated by the computer. The programmer needs to know how to interpret the hexadecimal error codes

33
Q

Disadvantages of ASCII code

A
  • Does not represent characters in non-Western languages
34
Q

What is the main disadvantage of high resolution images?

A

The increase in file size
As the number of pixels used to represent the image is increased, the size of the file will also increase. This impacts on how many images can be stored on, e.g. a hard drive. It also impacts the time to download an image from the internet or the time to transfer images from device -> device. A certain amount of reduction in resolution of an image in possible before the loss of quality becomes noticeable

35
Q

How many bytes in a kilobyte?

A

1000 bytes

36
Q

How many bytes in a megabyte?

A

1 000 000 bytes

37
Q

How many bytes in a gigabyte?

A

1 000 000 000 bytes

38
Q

How many bytes in a terabyte?

A

1 000 000 000 000 bytes

39
Q

How many bytes in a petabyte?

A

1 000 000 000 000 000 bytes

40
Q

How many bytes in an exabyte?

A

1 000 000 000 000 000 000 bytes

41
Q

How many bytes in a kibibyte?

A

1024 bytes (two to the power of 10)

42
Q

How many bytes in a mebibyte?

A

1 048 576 bytes (two to the power of 20)

43
Q

How many bytes in a gibibyte?

A

1 073 741 824 bytes (2 to the power of 30)

44
Q

How many bytes in a tebibyte?

A

1 099 511 627 776 bytes (2 to the power of 40)

45
Q

How many bytes in a pebibyte?

A

1 125 899 906 842 624 bytes (2 to the power of 50)

46
Q

How many bytes in a exbibyte?

A

1 152 921 504 606 846 976 bytes (2 to the power of 60)

47
Q

How do you calculate the file size of an image?

A

image resolution (in pixels) x colour depth (in bits)

48
Q

How do you calculate the size of a mono sound file?

A

sample rate (in Hz) x sample resolution (in bits) x length of sample (in seconds)

49
Q

How do you calculate the size of a stereo sound file?

A

The same equation as a mono sound file, then multiply the result by two

50
Q

Why is it necessary to compress the size of a file?

A
  • To save storage space on devices such as the hard disk drive/ solid state drive
  • to reduce the time taken to stream a music or video file
  • to reduce the time taken to upload, download or transfer a file across a network
  • the download/upload process uses up network bandwidth- this is the maximum rate of transfer of data across a network, measured in bits per second. This occurs whenever a file is downloaded, for example, from a server. Compressed files contain fewer bits of data than uncompressed files and therefore use less bandwidth, which results in a faster data transfer rate
  • reduced file size also reduces cost. For example, when using cloud storage, the cost is based on the size of the files stored. Also an internet service provider (ISP) may charge a user based on the amount of data downloaded
51
Q

Lossy file compression

A

With this technique, the file compression algorithm eliminates unnecessary data from the file. This means the original file cannot be reconstructed once it has been compressed.

Lossy file compression results in some loss of detail when compared to the original file. The algorithms used in the lossy technique have to decide which parts of the file need to be retained and which parts can be discarded

52
Q

Lossy file compression applied to an image

A

It may reduce the resolution and/or the bit/colour depth

53
Q

Lossy file compression applied to a sound file

A

it may reduce the sampling rate and/or the resolution

54
Q

What are common lossy file compression algorithms?

A
  • MPEG-3 (MP3) and MPEG-4 (MP4)
  • JPEG
55
Q

Lossy file compression: MPEG-3 (MP3)

A

MP3 files are used for playing music on computers or mobile phones. This compression technology will reduce the size of a normal music file by about 90%. While MP3 music files can never match the sound quality found on a DVD or CD, the quality is satisfactory for most general purposes

56
Q

In lossy file compression, how can the original music file be reduced by 90% while still retaining most of the music quality?

A
  • Removal of sounds outside the human ear range
  • if two sounds are played at the same time, only the louder one can be heard by the ear, so the softer sound is eliminated. This is called perceptual music shaping
57
Q

Lossy file compression: MP4

A

MP4 files are slightly different to MP3 files. This format allows the storage of multimedia files rather than just sound- music, videos, photos and animation can all be stored in the MP4 format. As with MP3, this is a lossy file compression format, but it still retains an acceptable quality of sound and video. Movies, for example, could be streamed over the internet using the MP4 format without losing any real discernible quality.

58
Q

Lossy file compression: JPEG

A

When a camera takes a photograph, it produces a raw bitmap file which can be very large in size. These files are temporary in nature. JPEG is a lossy file compression algorithm used for bitmap images. As with MP3, once the image is subjected to the JPEG compression algorithm, a new file is formed and the original file can no longer be constructed

59
Q

What concepts is the JPEG file reduction process based on?

A
  • Human eyes don’t detect differences in colour shades quite as well as they detect differences in image brightness (the eye is less sensitive to colour variations as it is to variations in brightness)
  • by separating pixel colour from brightness, images can be split into 8 x 8 pixel blocks, for example, which then allows certain ‘information’ to be discarded from the image without causing any real noticeable deterioration in quality
60
Q

Lossless file compression

A

With this technique, all the data from the original uncompressed file can be reconstructed. This is particularly important for files where any loss of data would be disastrous (e.g. when transferring a large and complex spreadsheet or when downloading a large computer application).
Lossless file compression is designed so that none of the original detail from the file is lost

61
Q

Run-length encoding

A

Run-length encoding (RLE) can be used for lossless compression of a number of different file formats:
- it is a form of lossless/reversible file compression
- it reduces the size of a string of adjacent, identical data (e.g. repeated colours in an image)
- a repeating string is encoded into two values:
- the first value represents the number of identical data items (e.g. characters) in the run
- the second value represents the code of the data item (such as ASCII code if it is a keyboard character)
- RLE is only effective where there is a long run of repeated units/bits

Computer science GCSE (13 decks)

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