Buried inside the Options Dialog box is a little check mark that can affect the way your files are stored and size limits of individual objects.
People use AutoCAD for many things. Most of the time, objects storage sizes are small. But sometimes things can get quite large.
Individual objects use to have a limit of 256MB – have you ever drawn anything that big? You may have with a mesh or an extremely large hatch pattern. Maybe by mistake you have had AutoCAD chunk away at creating something like a hatch and have it choke because it is too large.
Now you can avoid that… but it might cost you if you are saving files back to prior releases.
Here is the story from Autodesk…
The following explains how object size limits for drawings is determined:
Drawing files cannot exceed an internal size limit of 4GB. This size is based on the total size of all objects in a drawing when uncompressed. Since a drawing file is normally compressed, the final size of a saved drawing file on disk will vary based on the size and number of objects in a drawing.
Each individual object in a drawing cannot exceed an uncompressed size limit of 256MB. For example, a mesh object, when saved to a file and compressed, might be 75MB in size while the same object when uncompressed might be 257MB.
In these situations, the drawing cannot be saved to an AutoCAD 2007 or earlier file format until the issues are resolved. You can resolve the size limits by breaking the drawing or objects up into several drawings or objects.
Specifies whether or not the AutoCAD 2009 and earlier object size limits are used instead of those for AutoCAD 2010. Click the information icon to learn more about object size limits and how they affect opening and saving a drawing. (LARGEOBJECTSUPPORT system variable)
In the Options Dialog
The variable that is controlled by this is LARGEOBJECTSUPPORT
Controls large object size limit support when you open and save drawings.
0 = Use legacy object size limits from AutoCAD 2009 and prior
1 = Use AutoCAD 2010 object size limits
Drawings saved to a legacy drawing file format (AutoCAD 2007 or earlier) do not support objects greater than 256MB. With the AutoCAD 2010 drawing file format, these limitations have been removed allowing you to save objects that are greater in size.
When saving to a legacy drawing file format (AutoCAD 2007 or earlier), the drawing cannot contain large objects; there might be compatibility issues with trying to open the drawing. The LARGEOBJECTSUPPORT system variable controls the large object size limits used and the warning messages displayed when a drawing is saved.
Note: When working with the 64-bit release of AutoCAD, you can work more efficiently with large objects and drawings. However, the drawing files you create might be too large to open with the 32-bit release of AutoCAD.