.BK1 File Extension

Backup file created by Autodesk products, including AutoCAD Mechanical, Mechanical Desktop, and AutoCAD Map; stores a .BAK file that has been renamed with the ".bk1" extension; renamed when the Autodesk program terminates unexpectedly.

BAK files are automatically created when users save drawing files. Therefore, when a program crashes, Autodesk applications try to rename the BAK file to BK1 to prevent a corrupted drawing file from replacing the original backup.

NOTE: If the BK1 extension is already in use, Autodesk programs use ".bk2" through ".bk9," as well as ".bka" through ".bkz" and ".baa" through ".bzz" until a unique extension is found.

File created by Indexing Service, a component of Windows used to automatically index file system search information; contains information used for making fast file searches in Windows; typically seen with the name propstor.bk1.

BK1 files are often located within the C:\​System Volume Information\​catalog.wci\​ directory. Other catalog index files in this directory may include .BK2, .PS1, .PS2, .FID, .000, and .HSH files.

NOTE: Windows may also create BK1 files on external drives, such as USB flash drives.

Backup file created by ERwin Data Modeler, a data modeling program; contains a backup of a .ER1 diagram file; created automatically by ERwin when the ER1 file is opened; used to recover a data model file if the original becomes corrupted.

BK1 files are used by older versions of ERwin Data Modeler.