.BK1 File Extension
File Type 1Autodesk Backup File
What is a BK1 file?
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 Type 2ERwin Backup File
.BK1 File Association 2
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.
File Type 3Windows Indexing Service File
.BK1 File Association 3
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.
NOTE: Windows may also create BK1 files on external drives, such as USB flash drives.