DirectX is a collection of Application programming interface ( API ) from Microsoft for programming tasks related to all sorts of rich Multimedia content like game programming, Video and audio. Originally all the APIs were known by separate names as per their functionality e.g. DirectMusic, DirectPlay, DirectDraw etc.
The Alphabet ‘X’ was used so that the same name DirectX could be used for all the APIs and soon it became the name of the whole collection.
The ‘X’ that forms the base of the name of the Microsoft’s gaming console Xbox indicates that the console is based on the DirectX technology.
The first version of DirectX was released in September 1995 as the Windows Games SDK. DirectX was Included with Windows 95 OEM Service Release 2. Every version of Windows ever released since has been shipped with DirectX. DirectX 10 was a major update to DirectX API. DirectX 10 is available only with Windows Vista and later. DirectX 11 was also a major update and was unveiled in Gamefest 08 by Microsoft. DirectX 11 had improved multi-threading support to better utilize the multi-core processors. DirectX 11.1 is included in Windows 8 with a lot of improved component libraries. OpenGL is one of the popular alternatives to DirectX.