a search from google brought this:
http://www.xfree86.org/snapshots/3.9.15/RELNOTES1.html
in section 1.6:
1.6. Xinerama
Xinerama is an X server extension that allows multiple physical screens to
behave as a single screen. With traditional multi-head in
X11, windows cannot span or cross physical screens. Xinerama removes this
limitation. Xinerama does, however, require that the
physical screens all have the same root depth, so it isn't possible, for
example, to use an 8-bit screen together with a 16-bit screen in
Xinerama mode.
Xinerama is not enabled by default, and can be enabled with the +xinerama
command line option for the X server.
Xinerama was included with X11R6.4. The version included in this snapshot
contains many bug fixes. This is an area that we are still
working on, and we expect it to be improved further in future snapshots.
Known problems:
The Xinerama layout doesn't match the layout specified in the config
file's ServerLayout section.
It appears that there are still some bugs that cause unexpected
behaviour from time to time.
Most (all?) window managers are not Xinerama-aware, and so some
operations like window placement and resizing might not
behave in an ideal way. This is an issue that needs to be dealt with
in the individual window managers, and isn't specifically an
XFree86 problem.
-ben
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in lake'ch, my kin... 4 Ix
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