Data storage and compression — GCSE Computer Science practice questions

Question 1

A new laptop's specification sheet lists sizes in several units.

Which list shows the units in order from smallest to largest?

Accepted Answer

D: nibble, byte, MiB, GiB, TiB, PiB. A nibble (4 bits) is smaller than a byte (8 bits). After that, each unit is 1024 times the previous one: KiB, MiB, GiB, TiB, PiB, EiB. So the correct order is nibble, byte, MiB, GiB, TiB, PiB.

Question 2

A stadium's LED sign stores each row of lights with run-length encoding. Each run is written as the number of lights followed by the colour: G = green, W = white.

One row is stored as:

4G2W1G3W

Which row of lights does this represent?

Accepted Answer

B: GGGGWWGWWW. Each pair gives a run: 4G = GGGG, 2W = WW, 1G = G and 3W = WWW. Written in order this is GGGGWWGWWW, ten lights in total.

Question 3

A music-streaming app has a 'data saver' mode that sends songs compressed with lossy compression, and a 'studio' mode that sends them compressed with lossless compression.

Which statement is correct?

Accepted Answer

D: Lossy compression usually makes a smaller file than lossless compression, but the data it removes cannot be restored.. Lossy compression permanently removes data, such as sounds people are unlikely to notice, so it gives much smaller files but the original can never be rebuilt. Lossless compression keeps all the data, so the original is restored exactly; run-length encoding is a lossless method.