WEBVTT 00:00:00.240 --> 00:00:08.840 In your quest for the highest frame rates, the prettiest textures, and the 00:00:05.279 --> 00:00:11.719 most karma in the PC master race 00:00:08.840 --> 00:00:16.560 subreddit, you decided to go with a multi-GPU setup for your new gaming rig. 00:00:14.719 --> 00:00:22.160 But when you fire up your games, you notice that the sick gains you're 00:00:19.199 --> 00:00:28.160 getting aren't really what you expected, especially after 00:00:24.359 --> 00:00:30.800 dropping so much money on your system. 00:00:28.160 --> 00:00:37.360 So, what's the deal with that? Well, this problem has plagued PC gamers for 00:00:33.440 --> 00:00:39.760 over a decade. Why don't you usually get 00:00:37.360 --> 00:00:44.719 double the performance from a dual card configuration or triple if you have 00:00:42.079 --> 00:00:49.360 three video cards? I mean, since graphics rendering benefits from having 00:00:46.879 --> 00:00:53.520 more computing units in parallel, which you can learn more about in this video, 00:00:51.440 --> 00:00:59.199 by the way, wouldn't it make sense then for multicard setups like SLI and 00:00:56.079 --> 00:01:01.280 Crossfire to scale pretty easily? 00:00:59.199 --> 00:01:06.560 Unfortunately, it's not quite that simple. For starters, using two separate 00:01:04.239 --> 00:01:11.840 graphics cards means they have to talk to each other somehow. You see, most 00:01:09.360 --> 00:01:17.960 modern multiGPU setups use something called alternate frame rendering, where 00:01:14.560 --> 00:01:20.960 each card renders every other frame 00:01:17.960 --> 00:01:23.360 separately. Sounds efficient, but for 00:01:20.960 --> 00:01:28.479 them to be pushed to your monitor in the right order, the cards have to sync up 00:01:25.920 --> 00:01:34.640 properly, creating a surprising amount of overhead for both the GPUs and the 00:01:31.680 --> 00:01:40.400 electrical communication paths or buses that link them. This overhead not only 00:01:37.840 --> 00:01:46.159 gets worse as you add more cards to your rig, but can even result in a very 00:01:43.360 --> 00:01:51.200 unpleasant phenomenon called micro stuttering, which often shows up even if 00:01:48.880 --> 00:01:58.960 you're getting lots of frames per second. You see, for smooth gameplay, 00:01:53.840 --> 00:02:02.159 you need not only high FPS, but good and 00:01:58.960 --> 00:02:04.880 consistent frame times, which is the 00:02:02.159 --> 00:02:09.840 amount of time that a given frame will remain on your screen. Poor 00:02:07.600 --> 00:02:14.720 synchronization between the cards can leave certain frames on your monitor for 00:02:12.480 --> 00:02:19.360 way longer than they should be, even if the total number of frames each second 00:02:17.040 --> 00:02:23.360 is very high. This can render certain games 00:02:20.599 --> 00:02:29.360 unplayable, even though your setup is more than powerful enough to run it on 00:02:26.360 --> 00:02:31.680 paper. And as if that wasn't enough, an 00:02:29.360 --> 00:02:37.599 even bigger problem is that it's very difficult for your GPUs to know what 00:02:34.800 --> 00:02:42.959 frame to render next since it depends heavily on what the player chooses to 00:02:40.080 --> 00:02:49.440 do. The real time nature of game rendering makes it tough to parallelize 00:02:46.319 --> 00:02:51.840 in certain games among multiple GPUs, 00:02:49.440 --> 00:02:56.879 even with alternate frame rendering, as there isn't always a second frame or 00:02:54.239 --> 00:03:02.720 even part of a predicted one for your second card to work on. Of course, it 00:03:00.160 --> 00:03:08.000 isn't all about the inherent limitations of your hardware. On the software side, 00:03:05.840 --> 00:03:13.280 some game developers have been able to code their games in a manner that makes 00:03:10.319 --> 00:03:18.720 it easier for multiple GPUs to split the workload, while others simply don't 00:03:15.920 --> 00:03:25.360 bother. With the difficulty in coding for a very small subset of customers, 00:03:22.319 --> 00:03:28.000 many devs don't see the point in sinking 00:03:25.360 --> 00:03:33.120 tons of time into making sure that their games will play nice with multicard 00:03:30.159 --> 00:03:38.480 systems. Some games even manage to have worse performance in these situations. 00:03:36.159 --> 00:03:43.920 And finally, you definitely shouldn't run out and buy multiple GPUs if you're 00:03:40.959 --> 00:03:50.400 rocking a multiple monitor setup and you want extra video memory or VRAM to store 00:03:47.280 --> 00:03:52.799 all of your textures. With SLI and 00:03:50.400 --> 00:03:58.640 Crossfire, you are limited only to however much VRAM is on one card because 00:03:56.080 --> 00:04:03.200 both GPUs need to be able to access the same information in memory in order to 00:04:00.720 --> 00:04:08.560 work properly in tandem, whatever it might say on the packaging. So, does 00:04:06.159 --> 00:04:13.599 this mean then that SLI and Crossfire are useless gimmicks and a complete 00:04:10.480 --> 00:04:15.840 waste of money? Well, no. Multicard 00:04:13.599 --> 00:04:22.720 setups will give you the best possible performance in certain use cases and can 00:04:19.759 --> 00:04:27.600 even make some games playable at very high settings and resolutions where they 00:04:25.120 --> 00:04:32.240 wouldn't otherwise be, even with the best single card on the market. Not to 00:04:29.759 --> 00:04:37.120 mention that multiGPU rendering may improve with new APIs like Vulcan and 00:04:35.240 --> 00:04:42.639 DirectX12, which by the way you can learn more about here. Just do your 00:04:39.280 --> 00:04:44.639 research before you buy as to what games 00:04:42.639 --> 00:04:49.440 see the greatest benefit. And remember to keep your expectations realistic. 00:04:47.680 --> 00:04:55.280 After all, you wouldn't expect to be able to drive twice as fast just because 00:04:52.160 --> 00:04:57.120 you bought two cars, would you? 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