Fri Apr 09, 2004 5:42 pm by Tawakalna
from MS Help & Support document -
"DirectX provides access to the capabilities of your display and audio cards, which enables programs to provide realistic three-dimensional (3-D) graphics and immersive music and audio effects. DirectX is a set of low-level Application Programming Interfaces (APIs) that provides Windows programs with high-performance hardware-accelerated multimedia support.
DirectX enables the program to easily determine the hardware capabilities of your computer, and then sets the program parameters to match. This allows multimedia software programs to run on any Windows-based computer with DirectX compatible hardware and drivers and ensures that the multimedia programs take full advantage of high-performance hardware.
DirectX contains a set of APIs that provide access to the advanced features of high-performance hardware, such as 3-D graphics acceleration chips and sound cards. These APIs control low-level functions, including two-dimensional (2-D) graphics acceleration; support for input devices such as joysticks, keyboards, and mice; and control of sound mixing and sound output. The low-level functions are supported by these components that make up DirectX:
Microsoft DirectDraw
The Microsoft DirectDraw API supports extremely fast access to the accelerated hardware capabilities of a computer's video adapter. It supports standard methods of displaying graphics on all video adapters, and faster, more direct access when using accelerated drivers. DirectDraw provides a device-independent way for programs, such as games and 2-D graphics packages, and Windows system components, such as digital video codecs, to gain access to the features of specific display devices without requiring any additional information from the user about the device's capabilities.
Microsoft Direct3D
The Microsoft Direct3D API (Direct3D) provides an interface to the 3-D rendering functions built into most new video adapters. Direct3D is a low-level 3-D API that provides a device-independent way for software programs to communicate with accelerator hardware efficiently and powerfully. Direct3D includes support for specialized CPU instructions sets, providing additional acceleration on newer computers.
Microsoft DirectSound
The Microsoft DirectSound API provides a link between programs and an audio adapter's sound mixing, sound playback, and sound capture capabilities. DirectSound provides multimedia software programs with low-latency mixing, hardware acceleration, and access to the sound device. It provides this feature while maintaining compatibility with existing device drivers.
Microsoft DirectMusic
The Microsoft DirectMusic API is the interactive audio component of DirectX. Unlike the DirectSound API, which captures and plays digital sound samples, DirectMusic works with digital audio, as well as message-based musical data that is converted to digital audio either by your sound card or by its built-in software synthesizer. The DirectMusic API supports input in Musical Instrument Digital Interface (MIDI) format, and supports both compressed and uncompressed digital audio formats. DirectMusic provides software developers with the ability to create immersive, dynamic soundtracks that respond to a variety of changes in the software environment, not the least of which is direct user input.
Microsoft DirectInput
The Microsoft DirectInput API provides advanced input for games and processes input from joysticks as well as other related devices including the mouse, keyboard, and force-feedback game controllers.
Microsoft DirectPlay
The Microsoft DirectPlay API supports game connections over a modem, the Internet, or LAN. DirectPlay simplifies access to communication services and provides a way for games to communicate with each other, independent of the protocol, or online service. DirectPlay provides lobbying services that simplify the initialization of a multiplayer game, and supports reliable communication protocols to ensure that important game data is not lost on the network. New in DirectPlay 8.0 is support for voice communication over the network, which will significantly improve the playability of multiplayer team-based games, and add a new dimension to social games by providing the capability to talk to other people playing the game.
Microsoft DirectShow
The Microsoft DirectShow API provides high-quality capture and playback of multimedia files located on your computer and on Internet servers. DirectShow supports a wide variety of audio and video formats, including Advanced Streaming Format (ASF), Audio-Video Interleaved (AVI), Digital Video (DV), Motion Picture Experts Group (MPEG), MPEG Audio Layer-3 (MP3), Windows Media Audio/Video (WMA/WMV), and WAV files. DirectShow enables video capture, DVD playback, video editing and mixing, hardware accelerated video decoding, and tuning of broadcast analog and digital television signals."
basically it allows your o/s more direct access to your multimedia hardware thus making, amongst other things, the acceleration of your video and sound adaptors. That's why modern games look cr*p or won't play with the wrong version of DirectX.