1 00:00:00,000 --> 00:00:05,120 Bifurcation. It's a fancy word that means to split something into two, and today we're 2 00:00:05,120 --> 00:00:10,440 gonna talk about bifurcating something that isn't a sandwich, a sporting event, or a marriage. 3 00:00:10,440 --> 00:00:15,840 This episode is all about PCI Express Bifurcation. This is exactly what it sounds like, taking 4 00:00:15,840 --> 00:00:21,400 a PCI Express slot and chopping it up so that you can use multiple devices inside of it. 5 00:00:21,400 --> 00:00:26,480 But how does that work? I mean, you can't exactly shove two graphics cards in one slot. 6 00:00:26,480 --> 00:00:32,080 So the thing to keep in mind here is how PCI Express lanes are configured on modern platforms. 7 00:00:32,080 --> 00:00:38,080 Your CPU has a certain number of controllers, and each one can only support one device. 8 00:00:38,080 --> 00:00:43,840 For example, even though a current Intel CPU supports 16 lanes, it's split up with four 9 00:00:43,840 --> 00:00:49,960 controllers controlling four lanes each, meaning you can connect a maximum of four PCI Express 10 00:00:49,960 --> 00:00:55,080 devices. Of course, you can connect one graphics card and use all 16 lanes and just call it 11 00:00:55,080 --> 00:00:59,800 a day. But let's say that you want to use multiple PCI Express storage devices, like 12 00:00:59,800 --> 00:01:03,960 NVMe Solid State Drives. This is where bifurcation comes in. 13 00:01:03,960 --> 00:01:09,560 You see, one of the most common uses of bifurcation is when you want to connect several M.2 drives 14 00:01:09,560 --> 00:01:14,040 to a single PCI Express slot. This can be done using a fancy card that looks something 15 00:01:14,040 --> 00:01:18,600 like this, but here's the kicker. If you're gonna chop up just one slot, you need to tell 16 00:01:18,600 --> 00:01:24,400 your motherboard inside the BIOS exactly how to divvy up those lanes. Otherwise, it's just 17 00:01:24,400 --> 00:01:27,920 gonna see one of those four devices and you're gonna regret spending the money. 18 00:01:27,920 --> 00:01:31,960 How exactly you split up these lanes depends on what platform you're using. As mentioned 19 00:01:31,960 --> 00:01:36,240 earlier, the most you can do on a mainstream Intel platform is four devices with four lanes 20 00:01:36,240 --> 00:01:41,320 each. But on a server platform like AMD Epic, you might get something like eight devices, 21 00:01:41,320 --> 00:01:45,280 albeit with just two lanes each if you use that many. 22 00:01:45,280 --> 00:01:48,920 Bifurcation is a lot more common in enterprise settings, as data centers tend to use PCI 23 00:01:48,920 --> 00:01:53,920 Express lanes for things that you just wouldn't find at home, such as FPGAs and Asics. Chips 24 00:01:53,940 --> 00:01:58,980 and devices that can be highly customized to work on very specific kinds of operations. 25 00:01:58,980 --> 00:02:02,880 But that doesn't mean that there aren't additional uses for PCI Express bifurcation 26 00:02:02,880 --> 00:02:06,240 at home, like running two graphics cards in one slot. 27 00:02:06,240 --> 00:02:10,920 Although it's common for gamers to run just one graphics card at X16 speed, running a 28 00:02:10,920 --> 00:02:15,520 card at X8 will make virtually no difference to your performance as even high-end modern 29 00:02:15,520 --> 00:02:20,640 cards don't move enough data to really need those extra lanes. Now obviously, if you have 30 00:02:20,680 --> 00:02:25,840 a board with two free full-length PCI Express slots, lanes are automatically divvied up by 31 00:02:25,840 --> 00:02:30,400 a switch called a MUX chip so that each card runs at X8 speed. 32 00:02:30,400 --> 00:02:34,800 But there's actually nothing stopping you from sticking a two-slot riser card into 33 00:02:34,800 --> 00:02:40,920 your PCI Express X16 slot, plugging in two graphics cards with the help of riser cables 34 00:02:40,920 --> 00:02:45,240 and telling your BIOS to bifurcate the slot into two X8 connections. 35 00:02:45,240 --> 00:02:50,600 Just think, you could run NVLink on a one-slot mini-ITX board, assuming you could find a 36 00:02:50,600 --> 00:02:55,000 way to mount the cards in your case, so hopefully you don't mind using duct tape. 37 00:02:55,000 --> 00:02:59,300 But if you're interested in using PCI Express bifurcation, regardless of what exactly you'll 38 00:02:59,300 --> 00:03:04,760 be plugging in, you need to verify that your motherboard and BIOS support it. Not all motherboards 39 00:03:04,760 --> 00:03:09,480 allow you to enable it in the BIOS. And if that's the case, it's pretty much a showstopper, 40 00:03:09,480 --> 00:03:14,480 so do your research before you decide to turn your home rig into some sort of crazy science