Playback and Recording : Record Setup : Record Modes : Normal (Nondestructive) Record Mode

Normal (Nondestructive) Record Mode
In Normal, Nondestructive Record mode, Pro Tools records audio nondestructively, which means that if you record over a track’s existing clips, the audio is not erased from your hard drive. Both the new and old audio files remain on your hard drive, available as clips from the Clip List.
In Normal Record mode, the record range can be defined by selecting a range in a ruler or in a track’s playlist, or by specifying start and end points in the Transport window. If there is no selection, recording begins from the current Cursor location and continues until the Transport’s Stop button is clicked.
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To set a record range by selecting within a track’s playlist, the Timeline and Edit selections must be linked. See Linking or Unlinking Timeline and Edit Selections.
The pre- and post-roll settings allow material to be heard up to and after the start and end points, which is useful when punch recording (see Audio Punch Recording Over a Specified Range).