Data Storage and File Compression

Question 1

Units of data storage

Answer 1

Bit
Nibble (4 Bits)
Byte (8 Bits)
Kibibyte (1024 Bytes)
Mebibyte (1024 Kibibytes)
Gibibyte (1024 Mebibytes)
Tebibyte (1024 Gibibytes)
Pebibyte (1024 Tebibytes)
Exbibyte (1024 Pebibytes)

Question 2

Define Compression

Answer 2

Compression is reducing the the size of a file so that it takes up less space on secondary storage.

Question 3

Benefits of compression

Answer 3

Less storage space required
Less bandwidth required
Shorter transmission time
Use of data allowance

Question 4

Characteristics of lossy compression

Answer 4

Lossy compression is when data is lost in order to reduce the size on secondary storage and is irreversible

Lossy can greatly reduce the size of a file but at the expense of losing quality

Question 5

Characteristics of lossless compression

Answer 5

Lossless compression is when data is encoded in order to reduce the size on secondary storage

Lossless compression is reversible, the file can be returned to its original state

Lossless can reduce the size of a file but not as dramatically as lossy

Question 6

Where is lossless compression appropriate?

Answer 6

Lossless can be used on all data but is more suitable for data where a loss in quality is unacceptable, for example documents

Question 7

Where is lossy compression appropriate?

Answer 7

Lossy is only suitable for data where reducing quality is acceptable, for example images, video and sound

Question 8

Run - Length Encoding

Answer 8

A form of lossless compression that reduces the file size of a string of adjacent, identical data.

Repeated string is encoded in two values:
- The first value is the number of identical strings
- The second value is the code of the data

It is only effective when there is long run of repeated units.

Question 9

Examples of lossy compression

Answer 9

JPEG / JPG, MP3, MP4, MOV

Question 10

Examples of lossless

Answer 10

PNG, GIF, WAV, MOV, ZIP