Microsoft DirectX is a collection of application programming interfaces (APIs) for handling tasks related to multimedia, especially game programming and video, on Microsoft platforms.
Although DirectX contains a number of sub-components, DirectX is frequently referred to interchangeably with its most popular component, Direct3D, which is used to render 3D graphics. However, in its current form, it does include components for 2D graphics Direct2D, audio XAudio2 and input XInput.
The DirectX SDK is included within the Windows SDK, in all versions past Windows SDK v8. Normally, the Windows SDK is installed with Visual Studio (any version past Visual Studio 2012), however, it can be installed separately. Previously, the DirectX SDK was available as a separate installation, the last separate release was made June 2010. Using these SDKs, developers can target Direct3D 9.0c, 10.x and 11.x. Direct3D 12.0 can be targeted only with the Windows 10 SDK.
The DirectX end-user runtime is now distributed through Windows Update. Since Windows 7, this is the only method of installing or updated DirectX - there are no standalone runtime installers available. For other versions of Windows, see here.