[rescue] SGI Indy questions
ansalmo at dsl.pipex.com
Sun Jan 12 05:29:40 CST 2003
> > What is the max video and max cpu for this box, and is it cheap/feasable
> > to obtain while parts are still available (that is if they are still
> > available)?
> The best video you can get is XZ.
Not entirely true! This is definitely the case for the low-end CPUs, but
the R5000's may be better off running the 24-bit XL - depends on the task.
Here's a quote from Ian Mapleson's excellent SGI info site
When SGI released the R5000 CPU for Indy, the intention was that people
would use the main CPU instead of the XZ accelerator board for 3D graphics
because the R5000 has a higher MFLOPS performance rating than the 4 GEs on
the XZ board set. A comparison is:
XZ Hardware 128
R5000 150MHz 300
R5000 180MHz 360
Thus, SGI renamed XL Indys which had R5000 CPUs to XGE (GE = Geometry
Engine, implying main the CPU is effectively a better GE system than the old
XZ). However, this was never made clear enough at the time and so you may
come across R5000 Indys with XZ boards. In such systems, geometry and
lighting calculations are always done by the XZ board, so the wonderful
MFLOP performance of the R5000 is being wasted. In other words, it is
perfectly possible for an R5000 XL Indy to thoroughly outperform an R5000 XZ
Indy (it depends entirely on the type of 3D task being computed).
Unfortunately, the reverse situation can also occur because in other
situations the hardware Z buffering is more important (what Indy lacks is an
option that's closer to XS24Z for Indigo, ie. 24bit and hardware Z, but
letting the main CPU do the geometry/lighting calulcations). Sometimes, an
R5000 XL can't offer good performance because of Z-buffer bottlenecks. The
interactions are too complex to make a general statement, but examine the
Performance Comparisons page for examples - your particular task may
correlate closely to one of the tests.
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