We can counteract this performance penalty by dedicating a secondary video card exclusively to PhysX, but how much does it actually help? I've long known the benefits of a dedicated PhysX card from personal experience, but until now I'd never tested them systematically.
Asrock z87 Extreme9ac
Gigabyte GTX Titan x2 (SLI)
Evga GTX 650
Passion Leads Army
Passion Leads Army is a Chinese multiplayer shooter that utilises a bunch of dx11 and PhysX effects. I did four runs of its benchmark utility in each of the four configurations.
Let's pause and reflect on what this means. In one scenario, the PhysX was being rendered by a humble, budget-oriented GTX 650. In the other scenario, the PhysX was being rendered by two Titans.........and the Titans lost.
Clearly, PhysX is best taken out of the main GPU pipeline. Yes, the Titans can handle PhysX on their own, but they do even better when they can concentrate on their main tasks, while a lowly but capable helper quietly tackles the PhysX off to the side.
Cryostasisis a notoriously demanding game that would frequently cause a stutter-thon on even high-end systems. How much this is due to the complexity of its PhysX effects (which were very impressive back in 2009 and still look good today) and how much is merely due to poor optimisation (overall, the game isn't particularly pretty and is set mainly in small enclosed areas with few NPCs) is up for debate. Either way, it's a perfect benchmark for our purposes.
Not much action in the minimum framerates, and only SLI received a meaningful boost in the maximum framerates. But our PhysX card provided a significant improvement to the average framerates in all tests.
So, it's a modest improvement (somewhat surprisingly, given how much of a bottleneck PhysX can be in this game). But the verdict is clear: adding a PhysX card undoubtedly improves performance is Cryostasis.
Overall, the Mafia II benchmark doesn't look particularly impressive by today's standards; the characters are wooden and the lighting and geometry seems a little simple. The main thing that stands out is the dynamic PhysX behaviour, which looked great in 2010, and still looks decent today.
This time around, the victory is not pure. But it is still most certainly a victory: maximum framerate means little, since average framerate is where you spend the vast majority of your time. It could be argued that the most important figure is actually minimum framerate, since this represents the lags and framerate drops that you notice most of all, and which can hinder the gameplay and cause loss of immersion.
Metro: Last Light
Now for one of the most demanding games of recent times, which makes use of lots of bells and whistles, as well as considerable use of PhysX.
Actually, not at all - at least not in SLI. Take a look at the following graphs, supplied by the Metro Last Light benchmark itself. They each show a single run, and look much the same as the graphs of the many other test runs I did.
The first thing you'll notice is the much thicker black lines on the SLI systems, revealing a much greater rate of framerate variability (ie. less smooth framerate). That's the downside of multi-GPU setups, unfortunately, and it seems particularly pronounced in Metro Last Light.
But beyond that, notice the large difference in the black line of both graphs once you introduce a PhysX card, especially in SLI. Without a PhysX card, the line jumps wildly all over the place, routinely making leaps of 50 fps or more in a single split second. With an added PhysX card, the graph has the same general shape - the same peaks and troughs - but with much less variation. Though the overall FPS is actually pretty similar, it's a much smoother ride.
I can confirm that this was very noticeable when watching the actual benchmarks. Without a PhysX card, the benchmark was so full of microstuttering I found it somewhat frustrating to watch. With a PhysX card, it was much better. Though still not perfect, the stutters were much less frequent, especially in the latter, more PhysX-intensive half of the benchmark.
The results are more of a mixed bag in single-GPU mode, which already has a much thinner line (less variability) than the SLI system. On the whole, adding a PhysX card significantly thins the black line out, improving framerate consistency. But, unfortunately, it also adds more occasional spikes and dips. Still, I'd call this a win for the PhysX card, given the significant average fps improvement, and thinner line overall.
Batman: Arkham Origins
The Batman: Arkham games have always made impressive use of PhysX, using them not just for splashy tricks, but to subtly enrich the general atmosphere of the gameworld. Origin stakes these a notch up, with dynamic snow, steam and fog that reacts to the player. Let's see how our dedicated GTX 650 holds up.
It seems that the disparity between the 650 and the Titan is just too great, with the humble 650 unable to contribute anything that a Titan can't already do better on its own. Batman: Arkham Origins is, at time of writing, the latest PhysX game on the market, and uses complex dynamic snow and turbulence effects that aren't often seen in other games.
Perhaps the baseline of GPU grunt required by these effects proved too much for the 650. But could a PhysX card have helped if the disparity between the cards was smaller? To test this, I disabled SLI and instead dedicated one of my Titans to PhysX. These new results are shown in red below.
Wow. With a Titan taken off SLI duties and devoted to PhysX, the performance went through the roof. Not so much in the max framerate department, strangely, but who cares - the minimum and average fps is way up (by 60% and 42%, respectively).
This is perhaps unsurprising, given how poor the SLI scaling is. That second Titan was barely adding anything in SLI mode, but once switched to PhysX mode, it was set free to do some actual heavy lifting. And judging by the massive fps improvement, the PhysX in this game is heavy lifting indeed.
So, we've learnt that a PhysX card can make a massive difference in Batman: Arkham Origins. But we've also learnt that a GTX 650 is too weak to be of much help to a GTX Titan. A scenario with a smaller gap between cards would surely perform more desirably. For example, a GTX 670 & GTX 650 combination would probably work well, and something like a GTX Titan & GTX 680 combination probably would also.
So, is a dedicated PhysX card worth it?
Surely, the answer is a resounding "Yes!".It makes a substantial difference to some of the most demanding games, is easy, and is relatively cheap (I bought my GTX 650 for just over a hundred bucks - a mere fraction of the small fortune I spent on my Titans!)
Despite PLA's massive framerate improvement, I actually consider the Metro: Last Light results to be the most exciting, as an SLI user. With a PhysX card, I found myself getting immersed in the action as if I was watching a movie, whereas previously, it had felt like watching a tech demo that was straining under its own weight.
Whether it's an old card from a previous upgrade cycle, or a new one that you've bought specially for the purpose, a dedicated PhysX card seems a very worthwhile upgrade to me.
Who should get a dedicated PhysX card?
As my results show, a PhysX card can be of great value to a high-end rig. Even adding a budget card to a high-end setup helped significantly in 4 out of 5 tests (and adding a stronger card would surely give you great results in 5 out of 5).
Those who already have 2 cards in SLI and are thirsty for more performance would be wise to consider a PhysX card before they consider going 3- or 4-way SLI, as it can make a large difference and, at least in Metro: Last Light, greatly reduce microstuttering. In fact, as Batman: Arkham Origins has shown us, in some cases those users would be better off switching one of their existing cards to PhysX.
Low- and mid-range users
After adding the GTX 650 to my system, I've been very pleased. But the results may well be even more impressive for people with mid- or low-end rigs. If a midrange GTX 650 can shine next to the two behemoths that are GTX Titan SLI (in 4 of 5 games at least), how much brighter would it shine next to, say, a GTX 670?
And for that matter, you won't need a GTX 650 to get nice results. A GT 630, GTX 470, or GTX 260 would probably all do just fine too. At least in 4 out of 5 of our tests, the main benefit of a dedicated PhysX card comes not from the heaping more brute power into your system. The mere act of removing the PhysX pipeline from your main card(s) seems to be what makes a substantial difference most of the time.
The whole thing is clearly moot if you rarely actually play PhysX games.
PhysX is not going anywhere soon, and is used in some great games, from both AAA and smaller developers. Still, only a minority of games utilise the tech, and most of those tend to be shooters or 'action games'. Few racing, RPG, or strategy games use it. Only you know how relevant PhysX is to your gaming experience.
Personally, I've found it to be well worth it, as some really great games use it, and to spectacular effect. Furthermore, PhysX often appears in very high-end games that use plenty of other advanced features, in which case you want to give your PC all the help it can get.
Not everyone's motherboard and/or power supply will support an additional graphics card.
Before you get a dedicated PhysX card, make sure your motherboard can handle another card. On many motherboards, a second graphics card will lower the PCIe speed from x16 to x8 per card. By most accounts, that's fine and presents a minimal difference. Some motherboards may actually accept a second card, but will downgrade the PCIe slots to x4 speed, which is said to be a much more significant drop.
Even though PhysX is different from SLI, it's handy to look at the SLI capabilities of your motherboard. SLI doesn't officially support speeds as low as x4, so if your motherboard officially supports SLI, you'll be good to go.In my case, my PhysX card was my third card, so I had to upgrade to a motherboard that officially supported three-way SLI.
Also, make sure your power supply can handle an extra graphics card. Chances are that it can, but use an online PSU calculator to check just in case.
Noise, Heat, and Space
Even if your system can handle an extra card, make sure that adding one won't be too much of a burden on the rest of your case. You can see in the photo higher up that I chose a low-profile card that wouldn't block the intake fan of my Titans (The Titans have a fan on their underside towards the right of the card - ie. under the green "GTX").
If I had used another full-width card for PhysX, it would have somewhat impeded the uppermost Titan's ability to cool itself, which would have prompted the Titan's fan to spin louder, and possibly also to throttle as it got too hot.
The most powerful low-profile card I could find was the EVGA GTX 650. To my dismay though, it is LOOOUD. I don't know if it's all 650s, or just the Evga one, but it was way louder than both the Titans combined, and was unreasonably noisy even at idle. In the end, I disabled its fan entirely and used some workarounds to compensate. Moral of the story: do your research when you buy a card, and consider the noise, heat, and space issues, and not just fps performance.
Having said that, I left the 650ti enabled during an entire playthrough of Arkham Origins, and the performance was great. I had the game totally maxxed at 1080p in 3Dvision, and very rarely dipped between 60fps (which in 3Dvision is actually 120fps). The few dips that did occur never felt like they were the result of PhysX. Flooding the scene with all sorts of smoke, fog and debris never appeared to dent the framerate, and my 650ti never seemed to go above 80% usage.
Summing it all up: Pros and Cons
Pros of getting a dedicated PhysX card
- Helps address what is frequently one of the greatest bottlenecks in gaming performance (PhysX)
- Will likely raise your frames per second
- Can reduce or eliminate stuttering or freezing
- Can give a performance boost to games that need it most (PhysX is often found in high-end games that use plenty of other demanding features, such as the Arkham and Metro series)
- Can be acomparatively cheap upgrade, or even free (if using an old card from a previous build)
- Can be a quick and easy upgrade (unlike, say, upgrading your motherboard, cooling, OS, or overclocking)
Cons of getting a dedicated PhysX card
- Only works on a minority of games
- PhysX tends to be used in only 2 or 3 genres of games
- May require a motherboard upgrade, which becomes costly and time-consuming
- May require a PSU upgrade, if your current PSU can't handle another card
- Will require installing another graphics card close or adjacent to your existing card(s), which may contribute to noise, heat, and space issues
- Will raise the power usage of your PC
- In certain particularly demanding games, may actually decrease performance unless the card is reasonably expensive (see Batman Arkham Origins results above)
- Can only be used on an Nvidia system (officially at least - apparently there is a workaround for AMD users)
Only you know if installing a dedicated PhysX card is right for you. But as you can see from the various charts above, the performance benefits are significant. I wholeheartedly recommend considering one as part of your next upgrade.
I first experienced the benefit of a dedicated PhysX card a couple of years ago when I added a GTX 580 to my GTX 680. Among other things, this transformed Alice: Madness Returns (with PhysX on "high") from an unplayable freeze-a-thon to a silky 60fps. I thought I'd no longer need dedicated PhysX with Titan SLI, but then I noticed frequent PhysX-based stuttering in Metro: Last Light.
After seeing the results of my testing, I'm convinced for good. As long as PhysX continues to be used in games, and as long as it continues to look so awesome, a dedicated PhysX graphics card will remain staple in my upgrade cycle.
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Dave is a longtime PC gamer and power-user. He spends more on his gaming rig than a reasonable person should. He founded the indie game studio Volnaiskra, and is the creative force behind Spryke, a beautiful, skill-based platformer for PC. It's awesome, and you should totally go and check it out.