Enabling undo is global and persistent; when this setting is enabled, you will be able to undo mesh editing changes for any part or assembly meshes during your session. The setting remains enabled during your next ABAQUS/CAE session as well. Disabling undo frees any memory associated with this setting and causes any existing undo or redo cache on any parts or assemblies to be lost.
To enable undo and set the size of the cache:
Enter the Mesh module.
From the main menu bar, select Mesh
Edit.
ABAQUS/CAE displays the Edit Mesh dialog box.
Tip:
You can also display the Edit Mesh dialog box using the 
tool, located at the bottom of the Mesh module toolbox.
Click Settings.
The Mesh Edit Undo Settings dialog box appears.
Toggle on Enable Undo to enable undo for mesh editing operations.
Enter a value in the Max total cache size field in units of millions of elements, and click OK.
Click OK to close the Edit Mesh dialog box.
