BK1 file extension

Autodesk products, such as AutoCAD Mechanical, Mechanical Desktop and AutoCAD Map backup file that was originally a BAK file, but has been renamed with the BK1 extension. This renaming is usually occured when the Autodesk application terminates unexpectedly. If the BK1 extension is in use Autodesk use BK2 through BK9 extensions to save backup.

ERwin Data Modeler (data modeling application) file with a backup of a ER1 diagram file. The file is generated automatically when the ER1 file is opened. The file can be used to restore a data model file in the original one becomes lost or corrupted. Only older versions of ERwin Data modeler use BK1 files.

Indexing Service (Windows component that is used for automatic indexing file system search information) file with information used to make fast file searches in Windows. The default filename for BK1 files is "propstor.bk1". BK1 files are stored in the "C:/System Volume Information/catalog.wci/" folder with other catalog index files such as BK2, PS1, PS2, FID, 000 and HSH files. BK1 files may also be created by Windows operating system on external drives, such as USB flash drives.