Quantisation
The [see page 2, conversion] of continuous analogue input into finite discrete bands.
This is essentially a rounding of infinite resolution values into something a computer can process without the need for infinite storage and processing.
The process of signal quantisation and sampling is often called PCM Pulse Code Modulation.
Mechanically this involves using a see page 3, counter to assign separate bits to a computer chip which the computer can then record and store.