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bifurcation it's a fancy word that means to split something into two and today

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we're going to talk about bifurcating something that isn't a sandwich a

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sporting event or a marriage this episode is all about pci express

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bifurcation this is exactly what it sounds like taking a pci express slot

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and chopping it up so that you can use multiple devices inside of it

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but how does that work i mean you can't exactly shove two graphics cards in one

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slot to answer we reached out to philip meyer from tian and we'd like to thank

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him for his contributions so the thing to keep in mind here is how pci express

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lanes are configured on modern platforms your CPU has a certain number of

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controllers and each one can only support one device for example even

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though a current Intel CPU supports 16 lanes it's split up with four

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controllers controlling four lanes each meaning you can connect a maximum of

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four pci express devices of course you can connect one graphics card and use

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all 16 lanes and just call it a day but let's say that you want to use multiple

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pci express storage devices like NVMe solid state drives this is where

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bifurcation comes in you see one of the most common uses of bifurcation is when

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you want to connect several m.2 drives to a single pci express slot this can be

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done using a fancy card that looks something like this but here's the

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kicker if you're going to chop up just one slot you need to tell your

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motherboard inside the BIOS exactly how to divvy up those lanes otherwise it's

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just gonna see one of those four devices and you're gonna regret spending the

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money how exactly you split up these lanes depends on what platform you're

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using as mentioned earlier the most you can do on a mainstream Intel platform is

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four devices with four lanes each but on a server platform like AMD epic you

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might get something like eight devices albeit with just two lanes each if you

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use that many bifurcation is a lot more common in enterprise settings as data

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centers tend to use pci express lanes for things that you just wouldn't find

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at home such as fpgas and asics chips and devices that can be highly

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customized to work on very specific kinds of operations but that doesn't

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mean that there aren't additional uses for pci express bifurcation at home like

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running two graphics cards in one slot although it's common for gamers to run

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just one graphics card at x16 speed running a card at x8 will make virtually

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no difference to your performance as even high-end modern cards don't move

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enough data to really need those extra lanes now obviously if you have a board

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with two free full-length pci express slots the lanes are automatically

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divvied up by a switch called a mux chip so that each card runs at x8 speed but

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there's actually nothing stopping you from sticking a two slot riser card into

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your pci express x16 slot plugging in

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two graphics cards with the help of riser cables and telling your BIOS to

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bifurcate the slot into two x8 connections just think you could run

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nvlink on a one slot mini itx board

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assuming you could find a way to mount the cards in your case so hopefully you

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don't mind using duct tape but if you're interested in using pci express

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bifurcation regardless of what exactly you'll be plugging in you need to verify

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that your motherboard and BIOS support it not all motherboards allow you to

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enable it in the BIOS and if that's the case it's pretty much a show stopper so

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do your research before you decide to turn your home rig into some sort of

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crazy science experiment big thanks to pia for sponsoring this video private

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thanks for watching guys if you liked this video give us a thumbs up hit subscribe and be sure to give us a

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mention in the comments with your ideas for topics that we should cover in the

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future