Monday, April 09, 2007

I'm not a fan of SLI/CrossFire

When it comes to video cards, I've always been in the "don't spend more than $200" school of thought. My logic is: video card technology moves so fast that paying a lot of money for the "first six months" of any new technology level is very expensive. Bless all of you who are early adopters - you're helping keep nVidia and ATI humming, but it's an expensive hobby to main an up-to-date machine.

This is one of my favorite tables (there is a similar one on Wikipedia for ATI). It shows performance of graphics cards and when they came out. Compare the GeForce 7950 GT2 and the GeForce 8800 GTS. If you want 24,000 MT/S of fill rate, you could buy a top-of-the-line two-cards-in-one-via-SLI 7950, but if you waited six months, a SINGLE intermediate-speed 8800 would give you the same thing while supporting DX10 shaders (e.g. geometry shaders, instancing, and all that awesome stuff). The 7950 GT2 apparently retailed at $600+, which was a real discount compared to actually chaining two separate 7950's together (that'd get you up around $850). Look on and you'll see that GeForce 8800 prices aren't that expensive (compared to an SLI combination). And the 7950 GT2's come down a lot from what it used to cost.

For another datapoint, compare the Geforce 7600's to the GeForce 6800's. The 6800 was the monster card when it came out, putting nVidia back in the number one spot. But the next-generation's intermediate range cards can do what was top-end before. (The 7600 can be had for a little over $100. Compare that to several hundred for the 6800 ultra about one year earlier.)

Simply put, you pay a huge premium to get a given performance level when it's new and top-end. Wait one generation of cards (by buying last-year's top end cards or this-year's middle-range cards) and you save a lot.

It's in this context that I don't believe that SLI makes a lot of sense. In an environment where (IMO, and my opinion only) the top-end video cards are already expensive for what they do, SLI simply makes the situation worse, by allowing you to spend double what the already-high-end cards cost to get performance that will be available in one card in the next generation.

To do the math, does it make sense to spend double the price on your video card to extend its useful life by six months? Only if you intend to change cards every six months.

(nVidia makes an argument that SLI allows developers to preview the next-gen hardware, and this is true. My strategy is different: simply run X-Plane slowly and assume that the next-generation hardware will go faster.)

I don't feel good about criticizing nVidia and ATI because overall I feel that their products provide an extraordinary value at a very good price, and the growth of performance in video cards has been astounding. Todays cards just hit it out of the park.

But to me SLI and CrossFire strikes me as a solution looking for a problem. They solve the problem of making the most expensive cards more expensive, but I don't think they're the best way to spend money on a flight simulation system. (Better might be to not buy at the "SLI/Crossfire" level of video cards, meaning spending $700+ on your video cards, but rather to go down a level and upgrade your motherboard/CPU more frequently.)

Some users email me asking for video card recommendations, in particular whether to buy an SLI/Crossfire configuration. The bottom line is, it depends on how much you value your money vs. your graphics card performance. If money is on object, and you want maximum speed, SLI configurations will provide the fastest performance (by some marginal amount). I believe that a good value lies below $200.

On the other side of the equation, I do recommend that everyone spend at least $100 if you're going to buy a video card at all. Below $100 the price cuts come from remaindering really old inventory and removing parts from the card to save cost. For the savings of $25 you might lose half your card's performance or half of its VRAM when you get down to the really cheap cards.

The other thing I tell users is the truth: no one at Laminar Research has an SLI system, so the reports we get on SLI come from users. Some users have told us they've gotten some benefit at very high FSAA levels. But at this point a single 8800 wll do the same thing. And SLI doesn't address CPU speed at all. Consider this list of features - nothing on the CPU side will get even remotely faster with SLI.

And in full disclosure: my two Macs have a Radeon X1600 Mobility, a Radeon 9600, and a GeForce 5200 FX sits on the shelf for testing purposes. (This isn't intentional bias toward ATI, it's what Apple ships.)


alpilotx said...

Another interesting part to consider - when investing in hardware - is RAM. Especially if you intend to use my forests ( For good visuals and more or less stutter free flying you should consider 2GB of RAM. If you want to see th full glory, you will need 3-4 GB of it (my new computer has 4GB of it - this way I have no swapping anymore, even in very densely forested alpine regions). Of course, it is not the way to go for everybody, but as memory is becoming cheaper by the day, more and more should consider this (for example buy a 100$ cheaper graphics card and instead invest that money in RAM ;-).

Benjamin Supnik said...

I agree completely - RAM vs SLI is one example of "system balance". The system is like a bucket-brigade - the slowest link slows the entire thing down. So you want to spend your money on the system component that's causing the most slowdown.

If you don't have enough physical RAM (indicated by any consistent virutal memory paging during flight), more RAM is the way to go. It's also really cheap compared to a new CPU, top-end video card, or motherboard. So if RAM is an issue, it's a no-brainer to upgrade.

But please note - RAM isn't terribly incremental. Once you have "enough" adding more RAM will probably do you no good. There may be cases when you can run higher settings with more RAM, but for a given settings level once you hit no-paging, more RAM won't help at all.

Eleazaros said...

I read another comparison of SLI versus Crossfire which left me with a slightly different impression of the "value" of these technologies.

The article at:

Outlines the differences in plain English but gives a radically different picture of the chances of these 2 technologies for adoption in the industry -- if you read it with a background like mine.

SLI requires applications to recognize and support that architecture and the drivers must recognize the applications "profile" to support it.

If a given SLI doesn't recognize an application, it drops back to "compatibility" mode where only 1 card does all the work -- total waste of money unless you keep up to date with your drivers any time you install or upgrade a new game or "SLI" application. This is the old Voodoo 2 driver story...

+Fire portion read as if it does not require special driver information to do it's job. It "just works" but you can configure how it supports applications.

Now I'm still learning/researching this stuff (again -- like every 5 years I get to "relearn" this stuff...) but I do have a rather extensive background in the computer industry and I've seen a lot of failures show up over time.

A "proprietary" method does tend to be faster when used in its proprietary fashion so I would expect SLI to outperform +Fire with applications that are recognized by SLI but if I don't want to spend a good deal of time chasing drivers and the like then I'd say I'd probably be better off with +Fire because SLI will not last if game manufacturers (especially on-line games) have to rely upon another company to release driver updates "on-demand" every time they "patch" their video engines.

That just doesn't work anymore.

Anonymous said...

This is so outdated. No longer applicable discussion to the SLI mode of operation. You need to update this. I was a user of the that bad ass 4870x2 video monster of a card from ATI and only dumped it for SLI configuration with 2 9800GTX+ cards. They are outperforming even a single ATI 4870x2 due to overheating. That card cost me 100.00 month in electric.....I think your reference to XPLANE not being able to benefit is absolutely wrong. If FSX can be improved (and its the worse architecture) certainly XPLANE could

Benjamin Supnik said...


1. It's a blog. It's not a wiki. It's not a user's manual. The post is from 2009. If you go digging out old posts, you're going to find old commentary.

2. The main point, which I think you completely missed, is probably still true. My points were:

a. The sweet spot on video cards is not at premium prices. Dual card solutions are virtually always in the premium price band.

b. Video cards have tracked Moore's law, so fill rate gains from more expensive cards or simply more cards will be available at a lower price point in the near future.

c. LR doesn't spend money optimizing for SLI or Crossfire.

All three of these things are still true.

If you disagree with me re: SLI, great. My opinion re: SLI is just that, an opinion, nothing more.

Re: X-Plane not being able to benefit, I am not sure precisely what you are referring to. I think the only claim I am making is that CPU-bound features aren't addressed by SLI, which is basically true. You can't get a higher OBJ count by sticking a second GPU in your system; just more fill rate.

jmdewey said...

I read this today so I turned on FRAPS and checked my frame rate in a certain heavy scenery area, took out one of my video cards, and ran it again. I gained frames per second, from 52-53, to 58-60. I am going to get a new CPU, next, before I think about buying a new video card. I was running two Nvidia 470's, EVGA super overclocked. It's not a problem with power because I have a new Corsair premium quality 850 watt supply.