DirectX 11 - a set of software modules and libraries, which are necessary for processing of graphic 2D and 3D objects. All gamers know first-hand that to run most modern games on Windows systems requires the latest version of this set. The components included in this kit are responsible for graphical effects such as shadows, fog, or realism of water. They also affect game optimization, audio streaming (in games and 3D applications), and mouse, keyboard, gamepad, and other peripherals. DirectX 11 itself is already built into Windows 8 (just like DirectX 10 in Windows Vista), so it remains easy to install the latest version of DirectX 9 on your computer, which is necessary to run games on all modern operating systems.
The video card itself plays an important role. It will determine the extent to which certain functions of a particular version of DirectX are supported. This information is most often indicated on the box or in the graphics card instructions.
Compatibility with different versions of Windows is of great importance: for example, DirectX 10 works best with Windows Vista SP2 and Windows 7, while DirectX 9.0c is designed for Windows XP SP2 (and the 10th and 11th versions in the original build simply won't start), but is also supported by Windows 8.
With the help of the dxdiag diagnostic tool (located in the folder c:\Windows\System32\) you can always find out which version of DirectX is already on your PC and which audio, input and screen drivers are involved. The Notes field (the Sound and Input tabs) shows all the problems found.
Keep in mind that some old toys can be run only on certain versions of this software. And most of the older versions of DirectX have not been supported by developers for a long time.