Michael’s Corner

Michael's Corner is a monthly publication written by Michael E. Beall, Autodesk Authorized Author and peripatetic AutoCAD trainer. Michael travels all over the USA, bringing his fantastic experience and great understanding of AutoCAD to his clients. Michael's Corner brings together many of the tips, tricks and methods developed during these training sessions for the benefit of all users.

Michael's Corner provides something for every AutoCAD user. Every month, a number of articles cover a wide range of topics, suitable for users at all levels, including "The Basics" for those just starting out. Essentially, the aim of Michael's Corner is to help all AutoCAD users work smarter and faster.

This month…

From the Vault

Originally published December 2007

Purpose Served: The .BAK, .SV$, and the .DWL

Disclaimer: The following coverage regarding the backup file, automatic save file and lock files is presented so you can be more aware of what AutoCAD does with these various file types and the purpose they serve. It is always recommended that you backup important drawings to alternative media. This is also presented in an effort to enable those of you without daily technical access or assistance a more complete understanding of these files so you can implement efficient "housecleaning" of your systems.

The BAK File: The BAK file is created from the current DWG when you Save the drawing. The BAK file defaults to the folder in which the related DWG file is saved. It is the same size as the drawing file from which it was generated.

The SV$ File: The Automatic Save file extension is SV$ (not the oft presumed AC$ which is a temporary file). You configure the time interval at which that file is saved in the Open and Save tab of Options. It is also the same size of the drawing file from which it was generated.

The DWL File: This is a lock file. I frequently refer to it as the little "traffic cop" file that is created when a drawing is opened so if someone else opens that same drawing while it's open, they receive the "Read Only" notice. This is only 1KB.

They all do their job, to be sure, but several months down the road, do you really need them? Probably not, so consider this: Crackerjack IT personnel notwithstanding, at any given time, on your system you have roughly three times the file size for every drawing out there.

Both the BAK and SV$ files are there to "save the day" if you have a system crash. Beginning with A2006, when you launch AutoCAD after having a system crash, the Drawing Recovery manager appears with the names and related files of the drawings open at the time of the crash (see November 2005 Basics).

As for the little DWL file, it will automatically go away when the drawing it was locking is closed. If there's a system crash (or any other "illegal exit" of a drawing), it sticks around since it never received the official notice the drawing is closed.

All of that is wonderful, but if you still have BAK, SV$ (and to a lesser extent, DWL files) on your computer or server that are older than, say, three months, I would seriously consider deleting them and getting that space back. In my travels I have seen customers whose systems were a bit sluggish and come to find out they have a very small purple wedge of "free space" when they looked at the properties of their C:\ drive. Just a thought.

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