AutoCAD 2011 was sold under a perpetual license model. If you own an original disc or a previously purchased digital license, you can still use it.
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Early integration for viewing large 3D datasets. System Requirements for 64-bit AutoCAD 2011 was sold under a perpetual license model
Autodesk offers a 30-day free trial of the latest AutoCAD, which features full backward compatibility for .dwg files created in the 2011 version. autodesk autocad 2011 64bit download full