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http://www.hardwareanalysis.com/content/article/1728/

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Nvidia SLI, SLI's back with a vengeance Jun 28, 2004, 07:30 AM

By: Sander Sassen

I'm sure many of you can remember the days of 3dfx, the first Voodoo
Graphics back in 1996 and about a year later the introduction of the
Voodoo2. Voodoo2 actually made sure that 3dfx reigned supreme for
quite some time as two cards could be combined in something called an
SLI, Scan Line Interleave, configuration. Each card rendered half of
the image scan lines which resulted in double the performance of a
single board and the ability to play OpenGL games such as Quake 2 in a
1024x768 resolution. To date no manufacturer has come up with a
similar concept simply because modern graphics accelerators are all
AGP based, there's no dual AGP motherboards and PCI simply doesn't
have the bandwidth to handle modern graphics accelerators. With the
arrival of PCI-E things have changed though, a number of workstations
motherboards featuring the Tumwater chipset will have dual PCI-E-x16
slots making dual graphics accelerators a possibility again. Nvidia
steps up to the plate today with the re-introduction of the SLI
concept on the GeForce 6800 series, again using the SLI moniker but
now with a different approach to the same principles that made Voodoo2
SLI a huge success.




Two PCI-E GeForce 6800 Ultra graphics cards running in a SLI
configuration.

Whereas Voodoo2 SLI used a ribbon cable to be connected between two
Voodoo2 cards internally and a pass through VGA cable externally to
distribute the analog signal Nvidia's implementation is all done in
the digital domain. Both 6800 series PCI-E cards are connected by
means of a SLI, Scalable Link Interface, dubbed the MIO port, a
high-speed digital interconnect which connects to a connector on top
of both cards. Through this MIO port both cards communicate to each
other and distribute the workload which is accelerated by dynamic
load-balancing algorithms. In essence the screen is divided vertically
in two parts; one graphics card renders the upper section and the
second graphics card renders the lower section. The load balancing
algorithms however allow it to distribute the load across the graphics
processors. Initially they'll both start out at 50% but this ratio can
change depending on the load. Although Nvidia has remained
tight-lipped about what makes their SLI implementation tick exactly it
is clear that both hard- and software contribute to making SLI work.
Most of the dynamic load balancing between the two graphics processors
is handled in software and thus SLI needs driver support, drivers
which are as of yet unreleased, to work.




The MIO port connector that is used to connect two PCI GeForce 6800s
together in SLI.

Exact performance figures are not yet available, but Nvidia's SLI
concept has already been shown behind closed doors by one of the
companies working with Nvidia on the SLI implementation. On early
driver revisions which only offered non-optimized dynamic
load-balancing algorithms their SLI configuration performed 77% faster
than a single graphics card. However Nvidia has told us that
prospective performance numbers should show a performance increase
closer to 90% over that of a single graphics card. There are a few
things that need to be taken into account however when you're
considering buying an SLI configuration. First off you'll need a
workstation motherboard featuring two PCI-E-x16 slots which will also
use the more expensive Intel Xeon processors. Secondly you'll need two
identical, same brand and type, PCI-E GeForce 6800 graphics cards. For
workstation users it is also a nice extra that with a SLI
configuration a total of four monitors can be driven off of the
respective DVI outputs on the graphics cards, a feature we'll
undoubtedly see pitched as a major feature for the Quadro version of
the GeForce 6800 series SLI configuration.




The high-speed digital MIO port bridge connecting the two PCI-E cards
together.

The dual PCI-E-x16 motherboard however will mean a significant
investment, two PCI-E GeForce 6800GT cards could however make more
sense than a single PCI-E GeForce 6800 Ultra or Ultra Extreme, as the
performance increase will be much larger. Also, workstation
motherboards run at a hefty price premium over consumer products,
fortunately they do not require dual Xeons, a single Xeon will work
just as well. All in all Nvidia's SLI implementation brings back fond
memories of the 3dfx days and has all the right ingredients to once
again revolutionize 3D graphics provided you're willing and able to
pay the hefty price tag associated with it. Unlike Voodoo2 there's no
simple upgrade to double your 3D performance; apart from a second
PCI-E GeForce 6800 you'll need a new motherboard, memory and CPU(s).
That doesn't do much to dampen our spirits though, the best 3D
performance available comes at a price much like driving a Porsche or
Ferrari and it doesn't come cheap. Kudos to Nvidia for once again
raising the bar and making the harts of many gamers rejoice; SLI is
back, and with a vengeance.

Sander Sassen.
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I can't wait to see ATI's response to this. MAXX could be back!

don't forget that ATI has had the ability to scale upto 256
R300-Radeon 9700 VPUs since 2002. E&S and SGI have taken advantage of
this. now hopefully consumers can get in on the fun.

 

I know that some people seem to have a wad of cash just burning a hole in
their pocket, but how feasible are SLI graphic cards to the average
consumer? We're at a stage in computing where people realize that their
top-of-the-line system is considered "a starter system" within 18 months.
So, who's willing to shell out $500 or more for a SLI configuration when
they know that a better videocard is just around the corner? I mean dual
voodoo2's would have been kick ass back in the day, but their specs are
considered laughable compared to today's "entry level" 3D accelerators.

~ Jamie West

 

Believe me.... if they build and sell it people will buy it.