Xinerama v. TwinView

When it comes to a multi-headed environment under Linux, there
are two popular options for consumers — Xinerama and TwinView. Although
TwinView was developed by NVIDIA for allowing multiple monitors to be
powered by a single GPU with their array of GeForce graphics cards,
Xinerama was originally developed by Digital Equipment Corporation under
the name of PanoramiX, and was later incorporated into the X Window
System. Today at Phoronix, we have studied the frame-rate gaming
performance under multi-headed NVIDIA TwinView and Xinerama
configurations as well as a traditional single-head design.

Check out the full article over at Phoronix.