Formatting digital tapes
Data is recording on digital tape in a pre-defined pattern, sometimes known as the 'footprint'.
The rotary head of the recorder records diagonal stripes of data, including audio data, sub-codes, track-finding signals etc.
To create the footprint, the tape must be formatted.
In a DAT recorder, formatting always happens during recording. There is no separate formatting process.
ADAT and DTRS tapes can be formatted during recording, but it is more reliable and convenient to format tapes before recording takes place. Recorders of this type create a data section at the start of the tape, which can be used to store a table of contents and other data.
Each tape should be formatted all the way to the end, otherwise you will have a part-formatted tape in your possession. You could start recording, only for the recorder to drop out of record mode when it reaches the end of the formatted section.
Formatting erases any existing recording.
With all digital tapes, including DAT, the tape must be formatted continuously with no gaps in the footprint. If there is a gap, this might be interpreted as the end of the recording, even though there could be more material after the gap.