MA XIMUMPC SEPTEMBER 2004
nVidia Goes
Dual Card
What’s faster than one GeForce 6800 Ultra?
Two GeForce 6800 Ultras!QuickStart
The beginning of the magazine,
where articles are smallThe secret weapon of nVidia’s dual-
videocard rig is the as-yet-unnamed
bridge chip, which you can see
straddling the gap between these two
GeForce 6800 Ultras.This is the SLI connector, which
creates a high-speed interconnect
between the two PCI Express cards.
Note that the two connectors are a
fixed distance apart, so you need a
mobo with the right configuration
of PCI Express slots.In Maximum PC’s May issue, we broke
news of Alienware’s mysterious new
technology that promised to double
gaming performance by pairing two
identical PCI Express videocards and
letting them split the workload. The
Alienware solution requires a special
box to combine the signals from both
cards into a single signal that any
monitor can understand. Four months
later, nVidia has announced its own
dual-card solution, one that is even
more promising because it does the
exact same thing—without the special
box.
Like the Alienware rig, nVidia’s
dual-card solution requires two PCI
Express cards and a special Intel
Tumwater motherboard, required
because the Alderwood 925X chipset
includes just 16 high-speed PCI
Express lanes to its north bridge chip,
whereas Tumwater has 24 high-speed
lanes. (In order for a Tumwater board
to work properly, it needs two physical
x16 PCI Express slots, even if one of
them is running at just x8 speeds.)
Instead of using a special signal-
combining box, nVidia uses a high-
speed internal connector on the
videocards that allows them to share
necessary information. While nVidia
wouldn’t tell us exactly how fast the
interconnect between the two cards
is, we feel that using a dedicated
bus rather than leftover PCI Expressbandwidth should keep information
flowing between the cards without
robbing vital bandwidth between them
and the rest of the system.
We haven’t gotten our hands on
the new connector yet, but based on
photographs we’ve seen, it looks like
nVidia is using an actual board made
of silicon to connect the two graphics
accelerators. Be warned, however, that
this setup may be the cause of some
seriously slotty behavior. Because each
GeForce 6800 Ultra takes up one PCI
Express slot and blocks a regular PCI
slot, this configuration will consume a
whopping total of four slots!
Of course, the big question is: How
will the two competing technologies
from nVidia and Alienware
perform? nVidia claims its
dual-card solution runs almost
twice as fast as a single PCI
Express 6800 board. We have
no reason to doubt that. Our
hunch is that the nVidia
solution will actually be faster
than Alienware’s rig simply
because the nVidia cards will
use the custom interconnect to
communicate, instead of competing
with the rendering processes for
bandwidth across the PCI Express bus.
We expect to have a dual-PCI Express
rig in the Maximum PC Lab for testing
next month. Stay tuned for the results!