Quick questions on Data storage units and compression explained: O-Level Computing

The smallest unit is the bit (one binary digit). Eight bits make a byte. Above the byte, each unit is about $1000$ times the one below it (using the common decimal convention):

To estimate a file size, work out the total bits and convert to bytes. For an image, multiply the number of pixels by the colour depth:

Lossless compression reduces the size without losing any data, so the original file can be restored exactly. It works by storing information more efficiently, for example recording a repeated pattern once with a count. It is used where every bit matters: text documents, spreadsheets, program code and some image formats.

Lossy compression achieves much smaller files by permanently removing detail that a person is unlikely to notice, such as subtle colours in a photo or sounds the ear cannot easily hear. The original cannot be fully restored. It is used for photos, music and video, where a small loss of quality is an acceptable price for a much smaller file.

State how many bytes are in one megabyte, using the decimal convention. [2 marks]

Give two reasons a website might compress its images. [2 marks]

A file must be restored to its exact original after transfer. State which type of compression must be used and why. [2 marks]