Chapter 1 Data representation: Unit 1.3: Data Storage and File Compression

Question 1

Define bit

Answer 1

Basic unit of all computing memory storage terms and is either a 1 or a 0.

Question 2

What are the 7 sizes of bytes?

Answer 2

B - Byte
KB - Kilobyte
MB - Megabyte
GB - Gigabyte
TB - Terabyte
PB - Petabyte
EB - Exabyte

Question 3

Define nibble

Answer 3

Half a byte

Question 4

Define the IEC memory size system

Answer 4

IEC stands for International Electrotechnical Commission
Based on the binary system (powers of 2)

KiB - Kibibyte
MiB - Mebibyte
GiB - Gibibyte
TiB - Tebibyte
PiB - Pebibyte
EiB - Exbibyte

Question 5

What is the calculation for the file size of an image?

Answer 5

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

Question 6

What is the calculation for the file size of a mono sound file?

Answer 6

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

Question 7

Why are files compressed? (5 reasons)

Answer 7

To save storage space on devices such as the hard disk drive or 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 bandwidth - compressed files use up less bandwidth
Reduced file size also reduces costs

Question 8

Define bandwidth

Answer 8

The maximum rate of transfer of data across a network, measured in bits per second.

Question 9

Define lossy file compression

Answer 9

Eliminates unnecessary data from the file. The original file cannot be reconstructed once it has been compressed.
It may reduce the resolution and/or the bit/colour depth of an image file
It may reduce the sampling rate and/or the resolution of a sound file
Smaller than lossless files

Question 10

Define MPEG-3 (MP3)

Answer 10

MP3 files are used for playing music on computers or mobile phones
Lossy file compressed

Question 11

Define MPEG-4 (MP4)

Answer 11

Similar to MP3 files, but it allows the storage of multimedia files rather than just sound
It still retains an acceptable quality of sound and video, even though is it lossy file compressed.

Question 12

Define JPEG

Answer 12

Lossy file compression algorithm used for bitmap images.

Question 13

Define lossless file compression

Answer 13

Designed to compress the file, however none of the original detail from the file is lost.

Question 14

Define RLE

Answer 14

RLE (Run-length Encoding) can be used for lossless compression of a number of different file formats.
Is a form of lossless/reversible file compression
Reduces the size of a string of adjacent, identical data
A repeating string is encoded into 2 values:
- The first represents the number of identical data items in the run
- The second represents the code of the data item
Is only effective where there is a long run of repeated units/bits.