Hard Disk 40Mb (2001i) 80Mb (8.0) Variants There were multiple versions of the software release: 2001i 2001i Express 8.0 8.0 Express The Express versions did not support some features of the full software such as the use of bitmaps for rendering images. Threads were represented as cosmetics rather than geometry on the part. This limited use with say STL exports as the resultant exported surface in the data would be a smooth rod rather than a thread form. The 2008 Express release also removed support for Visual Basic for Applications (VBA) available in the 2001i version. The resolution of STL exports was also limited in the Express versions e.g. external diameters limited to 0.1° resolution in the export dialog box. Licensing License keys were required, for the Express variants which were obtained from the PTC website without charge. The returned keys (8 groups of 4 numeric digits) had expiry dates encoded to prevent use of the software after a certain date. The key obtained was based on data from the computer, which limited use of the key to the computer generating the license request. The key was based on the computers hard disk's Volume Serial Number (8 characters) and additional data about the computer (5 bytes). The number was passed to the web server in an obfuscated by alphabetic shift re-arrangement technique in order to make decoding of the transferred data more difficult. e.g. a Hard disk Volume ID of 0000-0000 would be encoded as petssssssssscs where the s is equal to the 0. Educational licensing Pro/DESKTOP had particularly distinguished itself in the education market. From a start in the CAD/CAM in Schools Initiative in the UK, Pro/DESKTOP has been donated free of charge to over 14,000 secondary schools worldwide, and is used by nearly 4 million students each school year. Its main educational rival was AutoCAD, which is widely used in secondary schools to teach 2D drafting and technical drawing. The use of Pro/DESKTOP in schools for 3D design has far exceeded AutoCad as it is generally considered too technical for the education market. Its minimal system requirements further cement the software as the program of choice for those just starting out in CAD. However, Pro/DESKTOP's user interface provides difficulty due to the lack of a multiple string undo function and the program's grouping of entities into work-planes that must have the same characteristics. Pro/DESKTOP is no longer available