Microsoft DirectX is a collection of application programming interfaces (APIs) for handling tasks related to multimedia, especially game programming and video, on Microsoft platforms. Originally, the names of these APIs all began with Direct, such as Direct3D, DirectDraw, DirectMusic, DirectPlay, DirectSound, and so forth. DirectX, then, was the generic term for all of these APIs and became the name of the collection. After the introduction of the Xbox, Microsoft has also released multiplatform game development APIs such as XInput, which are designed to supplement or replace individual DirectX components.

Direct3D (the 3D graphics API within DirectX) is widely used in the development of computer games for Microsoft Windows, Microsoft Xbox, and Microsoft Xbox 360. Direct3D is also used by other software applications for visualization and graphics tasks. In CAD/CAM engineering, for instance, it rivals the OpenGL by its ability to quickly render 3D graphics on DirectX-compatible graphics hardware. As Direct3D is the most widely publicized component of DirectX, it is common to see the names "DirectX" and "Direct3D" used interchangeably.

The DirectX software development kit (SDK) consists of runtime libraries in redistributable binary form, along with accompanying documentation and headers for use in coding. Originally, the runtimes were only installed by games or explicitly by the user. Windows 95 did not launch with DirectX, but DirectX was included with Windows 95 OEM Service Release 2. Windows 98 and Windows NT 4.0 both shipped with DirectX, as has every version of Windows released since. The SDK is available as a free download. While the runtimes are proprietary, closed-source software, source code is provided for most of the SDK samples.

The latest versions of Direct3D, namely, Direct3D 10 and Direct3D 9Ex, are only officially available for Windows Vista, because each of these new versions were built to depend upon the new Windows Display Driver Model that was introduced for Windows Vista. The new Vista/WDDM graphics architecture includes a new video memory manager that supports virtualizing graphics hardware to multiple applications and services such as the Desktop Window Manager

Components

The components comprising DirectX are

• DirectX Graphics, which consists of several APIs:
• DirectDraw: for drawing 2D Graphics (raster graphics). Now deprecated, though still in use by a number of games and as a video renderer in media applications.
• Direct3D (D3D): for drawing 3D graphics.
• DXGI: for enumerating adapters and monitors and managing swap chains for Direct3D 10 and up.
• DirectInput: for interfacing with input devices including keyboards, mice, joysticks, or other game controllers. Deprecated after version 8 in favor of XInput for Xbox360 controllers or standard WM INPUT window message processing for keyboard and mouse input.
• DirectPlay: for communication over a local-area or wide-area network. Deprecated after version 8.
• DirectSound: for the playback and recording of waveform sounds.
• DirectSound3D (DS3D): for the playback of 3D sounds.
• DirectMusic: for playback of soundtracks authored in DirectMusic Producer.
• DirectX Media: comprising DirectAnimation for 2D web animation, DirectShow for multimedia playback and streaming media, DirectX Transform for web interactivity, and Direct3D Retained Mode for higher level 3D graphics. DirectShow contains DirectX plugins for audio signal processing and DirectX Video Acceleration for accelerated video playback.