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Yesterday Dell announced its quad 7800GTX SLI motherboard, but is such a monstrosity something to really value, or is it the ultimate White Elephant?

When Michael Dell and Jen-Hsun Huang stood up in front of CES together and announced the Dell XPS 600 Renegade, a product manager for a major motherboard manufacturer began to laugh hysterically.  Dual 7800GTX video cards are nothing new -- I was shown several prototypes back in October.  Putting two of those cards in an SLI configuration is something that has been feasible for several months, but only on beta or severely hacked drivers.  NVIDIA's partnership with Dell means they will now need to provide quad SLI support inside the core Detonator drivers, or release specific drivers for these systems.  The first option leaves the possibility for some interesting driver hacks, the second option might not be practical depending on the actual volume of these systems.

But pragmatically looking at the performance of such a system, what can we really expect?  Many modern games only receive a 40% performance boost by putting 7800GT cards into dual SLI mode at modest resolutions, like 2048x1536.  Dual 7800GTX cards receive only about a 33% performance boost in the same benchmarks, but out of the gate a single 7800GTX out performs two 7800GT cards in SLI.

Diminishing returns is already apparent with only two high performance 7800GTX cards, and there are similar results elsewhere for 7800GTX 512MB cards.  Although there is no claim anywhere that this new XPS Renegade will be a mainstream system, hopefully we see more innovative and efficient (maybe even quiet) systems from the world's largest PC manufacturer, rather than another dirty hack to grab headlines... Fortunately Dell just released their 3007FPW to calm our tensions.

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RE: Not quite "diminishing returns"...
By Furen on 1/8/2006 1:32:35 AM , Rating: 2
Like I said, diminishing returns has nothing to do with cost. Diminishing returns, in itself, means that your benefit keeps lessening as you add additional units of input (in this case video cards) and at some point it will either reach 0 or you will have a disutility.

An example of this could be as follows:

You start with a single video card which gives you X performance. You add a second one and you get 1.8x performance. You add an extra pair (so you have 4) and you get 3x performance.

This implies that the marginal utility from adding the second card is .8x and the marginal utility for each of the third and fourth cards is .6x. From this you could deduct, with reasonable certainty, that the returns will continue to diminish until they reach zero and you start getting disutility as you add more and more cards. This is diminishing returns.

Regardless, system performance WILL experience diminishing returns because returns ALWAYS diminish in PCs because at the same time you are increasing the number of consumers (in this case video cards) you are splitting the rest of the resources between them. What I meant to point out is that the video subsystem is not at fault here for weak performance increase when going SLI with higher-end card, it's the CPU (and maybe memory subsystem) that will make performance drop. Some applications, in fact, will experience close to no performance diminishment.

By Motley on 1/8/2006 7:09:23 AM , Rating: 3
It depends on what you are considering for your "Units of input". You are looking at it as the number of video processors you are adding to the system, while I was looking at it as the amount of money I was tossing into it.

And I agree, the video subsystem is extremely powerful, and there probably is a very good use for it, but for 99% of the people out there, they won't be running that one application that scales that well over 4 video cores without being severely bottlenecked by the CPU, etc. Perhaps if it was in a Dual-processor system with 2 hyperthread enabled dual core P4's, and running some of the newer games that actually can use more than one core you'd see some difference. Maybe.

"And boy have we patented it!" -- Steve Jobs, Macworld 2007
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