AUTOSAVECHECKSONLYFIRSTBITDBMOD system variable
Ignore all but first bit of DBMOD for autosave
The first bit(1) of DBMOD means that the object database is modified. If this user preference is switched on, no autosave file will be created for files that are viewed only (DBMOD changes as soon as you pan and zoom).
Off (0): Autosave file for files that are viewed only
On (1): No autosave file for files that are viewed only