XFree86 4.2.1 is the first update to 4.2.0, the fifth full release in the XFree86 4 series.
Update releases are taken from a stable/maintenance branch. They are designed to be installed on top of the full release that they are updating. They contain fixes for serious problems, most commonly fixes for security issues, fixes for driver bugs, and fixes that improve stability.
XFree86 release 4 is a major re-design of the basic architectural underpinnings of XFree86's implementation of the original X Consortium's X Server. This re-design allows for a modular interaction between the hardware drivers and the XFree86 core X server. With 4.x, upgrades to the X server with new and unsupported hardware can be easily done and installed without undergoing the previous process of rebuilding an X server. All that is required is installing the new driver module and updating the configuration file.
The road to XFree86 release 4 began as an architectural concept in mid 1997, with the serious framework being implemented in code the beginning of 1998. There were several snapshots on the road to 4.0 which are now part of the 4.0 base release.
Release 4 also included the long-awaited integration of the DRI (Direct Rendering Infrastructure). This upgrade into the code base gives XFree86 the abilities of accelerated direct 3-D graphics rendering, used widely in games and other visualization programs.
While some driver available in the old 3.3.x release series have not been converted over to the 4.x series, those required for most modern video hardware are available. Please check the Driver Status document first to see whether your hardware is supported before upgrading to the 4.x series.
Specific release enhancements can be viewed in the Release Notes.
The XFree86 version numbering system has had some changes as of the 4.0.2 release. Information about this can be found in the Versions Document.
Information about binary distributions and the attendant installation instructions can be found in the Installation Document.
Copyright and Licensing information for this release and all XFree86 releases can be found in the License Document.