Mastercard-less Crossfire

[Neil]

Anyone managed MC-less Crossfire with two X1900GT's? It seems
that it is "well known" to be possible with the release of
Catalyst 6.6.

Anyone managed the same with an Intel 975X based mainboard?

I'm trying to decide what to buy next. I thought I knew, but
then the X1900GT came on the scene at about the same price
level[1] as the X1800XT (256MB), and I just saw some on-line
retailers have put up Conroe prices and they're cheaper[2] than
similar AMD parts.

Neil

[1] Though it seems to have gone up in price now.
[2] I never would have thought it.

 

[First of One]

Anyone managed MC-less Crossfire with two X1900GT's? It seems that it is
"well known" to be possible with the release of Catalyst 6.6.

Anyone managed the same with an Intel 975X based mainboard?

Nope, doesn't work:
http://forums.hexus.net/showpost.php?p=800296&postcount=15

Further down the thread, someone mentioned it only works on RD580 boards.
Without the dongle, all communication will be through the PCIe bus. The
975X's 2x8 PCIe layout may represent a severe IO bottleneck. While this
isn't proven, I think you'll need a board with 2x16 PCIe lanes to see any
significant performance gain over a single-card setup.

BTW, apparently ATi is using a bridge connector for its next-generation
parts.
http://www.dailytech.com/article.aspx?newsid=2794
So after a few years, it has come full circle... What ever happened to the
days when you can make an SLI bridge by taking a floppy cable and twisting
the four middle wires?

 

[Neil]

Nope, doesn't work:
http://forums.hexus.net/showpost.php?p=800296&postcount=15

I read that but I'd only seen the one person posting their
experience, and wondered/hoped there might be someone else who
"knew better".

Further down the thread, someone mentioned it only works on
RD580 boards. Without the dongle, all communication will be
through the PCIe bus. The 975X's 2x8 PCIe layout may represent
a severe IO bottleneck. While this isn't proven, I think
you'll need a board with 2x16 PCIe lanes to see any
significant performance gain over a single-card setup.

This article
(http://www.neoseeker.com/resourcelink.html?rid=125643) seems to
indicate that performance with 2x8 and 2x16 are pretty similar
and not that far behind a "proper" dongled Crossfire set up (in
most of the cases tested). Admittedly that was with X1800GTO's,
and I suppose that X1900GT's (given that they are based on a
"superior" processor) might be trying to pass more information
rather than less across the PCI-e bus. There was a detectable
difference between the three different Crossfire set-ups used,
and I guess that might become more marked with fancier cards.

BTW, apparently ATi is using a bridge connector for its
next-generation parts.
http://www.dailytech.com/article.aspx?newsid=2794

I'm not sure that's a step forward from using the PCI-e bus. I
mean, I'm sure it is in terms of performance, but unless you can
turn off Crossfire, but leave the cable in place, it would be
pretty inconvenient to have to open your case up to change over.
[ATM I can't see why I might want to turn it off, but I
understand that people do].

I get confused with all the R and RV numbers, where can I look
them up?

Neil

 

[First of One]

I read that but I'd only seen the one person posting their experience, and
wondered/hoped there might be someone else who "knew better".

To "test" dongle-less X1900GT Crossfire requires a bit of investment. i.e.
if it doesn't work, you'd have to return the second card.

(http://www.neoseeker.com/resourcelink.html?rid=125643) seems to indicate
that performance with 2x8 and 2x16 are pretty similar and not that far
behind a "proper" dongled Crossfire set up (in most of the cases tested).
Admittedly that was with X1800GTO's, and I suppose that X1900GT's (given
that they are based on a "superior" processor) might be trying to pass
more information rather than less across the PCI-e bus.

That was an interesting article. Learn something new everyday... It seems
the 2x8 setup suffers no real disadvantage over the 2x16 setup. And this was
with Cat. 6.5, which has PCIe optimizations that result in faster
dongle-less performance than before.

It'll be interesting to see a comparison with X1900GT cards. This site was
preparing an article on X1900GT master+slave card testing until the author
got word of the 6.6 drivers:
<http://www.pcinpact.com/actu/news/29573-CrossFire-de-X1900GT-on-se-passera-aussi-de-.htm>
Use Google or Babelfish if you can't read French.

Of course, if you are building a rig from scratch, a 7950GX2 seems like a
better deal. "Only" $560 at Newegg or mWave, it costs less than two
X1900GTs, uses less power, and you're not tied to any particular mobo.

I'm not sure that's a step forward from using the PCI-e bus. I mean, I'm
sure it is in terms of performance, but unless you can turn off Crossfire,
but leave the cable in place, it would be pretty inconvenient to have to
open your case up to change over.

One reason to turn off Crossfire is to use multiple monitors. Currently,
that's easily done in software through CCC. In fact, I imagine a few users
switch Crossfire on and off several times a day. The bridge shouldn't need
removal for any reason.

I get confused with all the R and RV numbers, where can I look them up?

You'll have to look them up one by one on Google. Generally R--- means
high-end. RV--- means value. RD--- means motherboard chipset.

 

[Neil]

It'll be interesting to see a comparison with X1900GT cards.
This site was preparing an article on X1900GT master+slave
card testing until the author got word of the 6.6 drivers.

I put in a support ticket at ATI.com asking about MC-less CF
support in 975X, and if not, which Conroe chipset would support
it. This was the answer:

# Solution: Currently the only supported Crossfire configuration
for X1900 series cards requires a Crossfire Edition card. There
are no announced plans from ATI for support of Crossfire with
two Crossfire Ready cards.

Which I thought was a bit odd. The idea of MC-less CF seems to
be all over various forums, including words which sound a lot
like "ATI have announced MC-less CF for all cards up to X1900GT
from Cat 6.6 onwards." And even on ATI's own site there is a
driver set (6.4Beta IIRC) specifically for download by people
who want to do MC-less CF with X1800GTO cards.

Of course, if you are building a rig from scratch, a 7950GX2
seems like a better deal. "Only" $560 at Newegg or mWave, it
costs less than two X1900GTs, uses less power, and you're not
tied to any particular mobo.

But you can't buy half a 7950GX2 at a time. I only checked one
retailer, but their cheapest 7950GX2 was £400.[1] When I first
saw X1900GT's they were about £140, the last time I noticed any
they were up around £180; that's still less than half the price
of the Nvidia beast. The no particular mainboard would be an
advantage, and I expect the Nvidia card is probably a better
performer too.

Neil

[1] Don't bother telling me where I can get one cheaper. Unless
it's less than half that price, it's not for me.

 

[First of One]

# Solution: Currently the only supported Crossfire configuration for X1900
series cards requires a Crossfire Edition card. There are no announced
plans from ATI for support of Crossfire with two Crossfire Ready cards.

Well, if you take a look at the release notes for the 6.6 drivers, there is
no mention of dongle-less CF functionality with X1900GTs. Of course, "not
supported" doesn't equal "not working".

Which I thought was a bit odd. The idea of MC-less CF seems to be all
over various forums, including words which sound a lot like "ATI have
announced MC-less CF for all cards up to X1900GT from Cat 6.6 onwards."

Has ATi actually announced this? Everywhere I read, all the reports point
back to the Hexus news tidbit. It's more likely just leaked information.
PCInpact also mentioned a Xpress 3200 (RD580) board would be required for
dongle-less X1900GT CF; this may or may not be credible.

And even on ATI's own site there is a driver set (6.4Beta IIRC)
specifically for download by people who want to do MC-less CF with
X1800GTO cards.

When the 6.6 Beta drivers were first posted,
http://forums.guru3d.com/showthread.php?p=1805984
There was a link at the bottom of the post:
http://www.distichannel.com/Chuck_for_CrossFire_Conroe.zip
It's meant to test HDR+AA in Oblivion with Crossfire on Conroe systems. This
may work for dongle-less X1900GTs, but I doubt anyone will risk spyware
infestation just to try it out.

But you can't buy half a 7950GX2 at a time. I only checked one retailer,
but their cheapest 7950GX2 was £400.[1] When I first saw X1900GT's they
were about £140, the last time I noticed any they were up around £180;

The 7950GX2 goes for $560 in the US, which is equal to £305. UK prices are
31% higher. Faced with those markups, I don't blame you for staying away.