DWG (from drawing) is a proprietary binary file format used for storing two- and three- dimensional design data and metadata. It is the native format for several CAD packages including DraftSight, AutoCAD, IntelliCAD (and its variants), Caddie and Open Design Alliance compliant applications. In addition, DWG is supported non-natively by many other CAD applications. The .bak (drawing backup), .dws (drawing standards), .dwt (drawing template) and .sv$ (temporary automatic save) files are also DWG files. DWG (denoted by the .dwg filename extension) was the native file format for the Interact CAD package, developed by Mike Riddle in the late 1970s, and subsequently licensed by Autodesk in 1982 as the basis for AutoCAD. From 1982 to 2009, Autodesk created versions of AutoCAD which wrote no fewer than 18 major variants of the DWG file format, none of which is publicly documented. The DWG format is probably the most widely used format for CAD drawings. Autodesk estimates that in 1998 there were in excess of two billion DWG files in existence.