BIM Software Tip: Understanding AutoCAD Backup and Auto Save Files
In AutoCAD, file backup (.bak) involves creating backup graphic files and manually saving your DWG files. By default, these backup files are saved in the same folder as the original drawing, sharing the same filename but with a .bak extension, such as site_topo.bak. This backup file is an exact copy of the most recently saved drawing, representing a version prior to the current one. Only one backup file is retained per drawing, so new backups will overwrite older ones with the same name.
Note: Backup files are only created if the system variable ISAVEBACK is set to 1.
Essentially, a backup file is a renamed DWG file. To restore data from a .bak file, simply rename its extension back to .dwg and open it in AutoCAD.
MOVEBAK Command
The MOVEBAK command, available through AutoCAD Express Tools, allows you to specify a different folder for storing backup files. Instead of saving backups in the same folder as your drawings, you can use MOVEBAK to automatically move all backup files to a designated location. To reset AutoCAD to its default behavior, enter ;.
Note: The MOVEBAK command is only available in Autodesk products that include AutoCAD Express Tools. Recent updates may limit support for folder paths containing spaces.
Auto Save (.sv$) Files
Auto Save files, typically with the extension .sv$, are automatically created backups generated by AutoCAD’s auto save feature. The auto save interval is enabled by default and can be adjusted in the Options dialog under the Open and Save tab, or by modifying the SAVETIME system variable.
If AutoCAD crashes or terminates unexpectedly during a task, the most recent data can be recovered from an .sv$ file. These files can be found automatically by AutoCAD, renamed with a .dwg extension, and then opened like regular drawings. The auto save file contains all graphic information saved during the last session. Normally, when AutoCAD closes properly, .sv$ files are deleted.
To locate the auto saved files, open the Options dialog, go to the Files tab, and check the path set for Automatic Save File Location. Use Windows Explorer to navigate to this folder to recover any .sv$ files.
Auto Save can be disabled by unchecking the option under the Open and Save tab or by setting the SAVETIME variable to 0.
Note: Disabling Auto Save prevents the automatic creation of .sv$ files, which means there will be no temporary backup files for data recovery in case of a crash.
By default, temporary files with an .ac$ extension are created during AutoCAD sessions. These files store information from various AutoCAD commands like Undo but do not contain repairable graphic data. They typically exist only if AutoCAD crashes or terminates abnormally.
Drawing Recovery Manager
Introduced in AutoCAD 2006, the Drawing Recovery Manager helps locate and open drawings that were active during a crash, including all associated backup and auto save files.
When you restart AutoCAD after a crash, the Drawing Recovery Manager identifies which drawings were open and crashed, displaying them along with their backup and auto save files in a single interface.
This tool allows you to open backup and auto saved files directly from AutoCAD without manually searching for or renaming them. Upon opening a recovered file for the first time, you will be prompted to save it under a new name.
Note: The Drawing Recovery Manager is only active after a crash and displays information related to the session during which the crash occurred. It cannot be launched during normal operations to view backups or auto saved files from the current session.
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