AutoCAD is a suite of popular CAD software products for 2- and 3-dimensional design and drafting, developed and sold by Autodesk. The AutoCAD family of products, taken as a whole, are the most widely used CAD software in the world.
Initially a general-purpose 2D drafting program, AutoCAD has evolved into a family of products which provide a platform for 2D and 3D CAD. Today, it is used by civil engineers, land developers, architects, mechanical engineers, interior designers and other design professionals.
Modern AutoCAD includes a full set of basic solid modelling and 3D tools, but lacks the advanced capabilities of solid modelling applications. AutoCAD can co-exist with such products as a 2D drafting tool.
Like other CAD programs, AutoCAD is fundamentally a vector graphics drawing program. It uses primitive entities — such as lines, polylines, circles, arcs, and text — as the foundation for more complex objects.
AutoCAD supports a number of application programming interfaces (APIs) for customization and automation. These include AutoLISP, Visual LISP, and VBA. AutoCAD’s license-based API, ObjectARX, can be used; a C++ class library, which was also the base for products extending AutoCAD functionality to specific fields, to create products such as Autodesk Architectural Desktop, AutoCAD Electrical, or third-party AutoCAD based applications.
AutoCAD’s native file format, AutoCAD DWG, and to a lesser extent, its interchange file format, DXF, have become de facto standards for interchange of 2D CAD data. In 2006, Autodesk estimated the number of active DWG files to be in excess of one billion. In the past, Autodesk has estimated the total number of DWG files in existence to be more than three billion.
AutoCAD currently runs exclusively on Microsoft desktop operating systems. Versions for Unix and Apple Macintosh were released in the 1980s, but these met with limited market acceptance and were later dropped. It usually suffers from poor performance when run in an emulator or compatibility layer like Virtual PC or Wine. 
AutoCAD LT is a “scaled down” version of AutoCAD. “LT” does not stand for “light”; it originally stood for “lap top”. (One pronounces the letters individually.) When AutoCAD LT was first introduced in 1993, laptop computers did not have the performance features they have today. A version of AutoCAD with a reduced feature set, and thus a smaller memory footprint, was needed for portable use. AutoCAD LT was the result.
Today, Autodesk sells AutoCAD LT for its much lower price. It is marketed as a CAD package for those who only need 2D functionality. Compared with the full edition of AutoCAD, AutoCAD LT lacks several features, has almost no 3D capabilities, and does not include any programming interfaces.
Overlay or Plug-in programs
Autodesk has also developed overlay or plug-in programs, sometimes called Desktops, for discipline-specific enhancements. Architectural Desktop, for example, permits architectural designers to draw objects such as walls, doors and windows, with more intelligent data associated with them, rather than simple objects such as lines and circles. The data can be programmed to represent specific architectural products sold in the construction industry, or extracted into a data file for pricing, materials estimation, and other values related to the objects represented. Similarly, Civil Design, Civil Design 3D, and Civil Design Professional allow data-specific objects to be used, allowing standard civil engineering calculations to be made and represented easily. Additionally, Autodesk Inventor allows the technician to design any moving object (or idea) and visually represent movements on screen.
- Version 1.0 (Release 1) – December 1982
- Version 1.2 (Release 2) – April 1983
- Version 1.3 (Release 3) – August 1983
- Version 1.4 (Release 4) – October 1983
- Version 2.0 (Release 5) – October 1984
- Version 2.1 (Release 6) – May 1985
- Version 2.5 (Release 7) – June 1986
- Version 2.6 (Release 8) – April 1987
- Release 9 – September 1987
- Release 10 – October 1988
- Release 11 – October 1990
- Release 12 – June 1992
- Release 13 – November 1994
- Release 14 – February 1997
- AutoCAD 2000 (v.u.15.0.02) – March 1999
- AutoCAD 2000i – July 2000
- AutoCAD 2002 (R16.1.01) – June 2001
- AutoCAD 2004 (v.u.18.1.01) – March 2003
- AutoCAD 2005 (v.u.19.1.01) – March 2004
- AutoCAD 2006 (v.u.20.1.01) – March 2005
- AutoCAD 2007 (v.u.21.1.01) – March 2006
- AutoCAD 2008 – 2007
Article credits: Content on this page came from various articles on en.wikipedia.org.