Jeff Morris | Sr. Applications Expert
Nostalgia?
Remember the “good old” days when AutoCAD was a single document interface? This meant that only one drawing could be opened at once. If one wanted to work on multiple drawings at once, one had to open multiple AutoCAD sessions.
I believe in the 2000 or 200i release of AutoCAD we were finally able to open more that one drawing per AutoCAD session, and what a relief that was.
Be careful what you wish for!
Sometimes though it is nice to have only one drawing open at once. For example, if I need to check many drawings, I find it more convenient to simply open the next drawing while simultaneously closing the current drawing.
Also, when writing scripts that open a list of drawings one at a time to perform some function, it is convenient to enable AutoCAD only to have one drawing open at once.
The SDI Variable.
There is a way to have your proverbial cake and eat it too!
The SDI variable can be enabled or disabled. SDI stands for Single Drawing (Document?) Interface. By typing in SDI at the command line, one can set it to 1 (which is enabled or On) or to 0.
If you want to get back to the “good old days”, set SDI to 1, which enables the Single Drawing Interface (which negates the Multiple Drawing Interface). Now when a change is made to your drawing and you go to open another drawing, you will be prompted to save your current drawing.
Depending on your answer, the drawing will or will not be saved, it will close and the next drawing will open.
Trivia anyone?
There was a time when SDI could also hold values of 2 or 3, although these values could not be entered by the user. It had to do with LDT (or LDD) – AutoCAD Land (Development) Desktop. When the special LDT commands were used, the drawing interface HAD to be set to 1, because LDT was writing specific information to an external database connected to the current drawing.
These two SDI options tried to accommodate this by providing some flexibility.
Here’s the official explanation:
0 Turns on multiple-drawing interface.
1 Turns off multiple-drawing interface.
2 (Read-only) Multiple-drawing interface is disabled because AutoCAD has loaded an application that does not support multiple drawings. SDI setting 2 is not saved.
3 (Read-only) Multiple-drawing interface is disabled because the user has set SDI to 1 and AutoCAD has loaded an application that does not support multiple drawings. (SDI was set to 1 before the application was loaded.) SDI setting 3 is not saved.
If SDI is set to 3, AutoCAD switches it back to 1 when the application that doesn't support multiple drawings is unloaded.
Conclusion
I routinely turn the SDI variable On (1) or Off (0) depending on my needs.
It is not so much a debate as to which is better, it is convenient to be able to work in either mode depending on ones needs.