so I've been reading up on SGI's architecture lately, and found this:
http://www.sgi.com/o2/uma.html

seems like a pretty cool idea... sharing the main memory between system and
video, so you don't need to copy data from main memory to video memory, just
pass a pointer to the data.

cheaper x86-based systems have allocated main memory for the video subsystem
in the past; but it's not quite the same thing. they just allocated a
contiguous chunk of memory for video, at boot time; rather than actually
*sharing* it. so if you wanted to access that memory, you needed to copy
data from/to it, from system memory, through the video subsystem. (AFAIK).

I have heard that the X-Box shares video memory with system memory... any
chance it does something like truly shared memory? Or is it just the crappy
old way to cut costs, by allocating a chunk for video, that isn't directly
accessible to the CPU?

I think this feature of the SGI O2 is one of the things they'll try to keep
for IRIX... I'd be really surprised if Linux and XF86 could take advantage
of this, any time soon. I'm sure it makes Quake2 look *really* good. :)

Carl Soderstrom
-- 
Network Engineer
Real-Time Enterprises
(952) 943-8700