TECH TALK Where Are the PCIe 4.0 Graph­ics Cards & Mo­bos?

It’s been over a decade since PCI-SIG an­nounced the pre­lim­i­nary specs for what would be­come PCIe 3.0, and we’ve been able to use Gen3 graph­ics cards since 2010. The PCIe 4.0 specs, tar­get­ing roughly dou­ble the band­width per pin of Gen3, started the next y

Maximum PC - - QUICKSTART - Jarred Wal­ton Jarred Wal­ton has been a PC and gam­ing en­thu­si­ast for over 30 years.

Go­ing a step fur­ther, PCI-SIG an­nounced the ini­tial plans for PCIe 5.0 along­side the Gen4 fi­nal specs, tar­get­ing 32GT/s per pin. Yet we still don’t have any PCIe 4.0 graph­ics cards or moth­er­boards.

It’s not that Gen4 so­lu­tions don’t ex­ist—IBM is ship­ping servers with PCIe 4.0 slots—but on the con­sumer side, not even Nvidia’s Tur­ing ar­chi­tec­ture sup­ports Gen4. That’s largely be­cause most con­sumer work­loads don’t need the ex­tra band­width. Gam­ing on a Gen3 x8 slot causes al­most no loss in per­for­mance, and with SLI and Cross­Fire see­ing less sup­port and use, we’ve been rest­ing on the 8GT/s plateau for years.

I said “most” con­sumer work­loads, as there are ar­eas where we’d ben­e­fit from Gen4’s added band­width. In­tel’s main­stream con­sumer CPUs have 20 Gen3 PCIe lanes, with four used for the DMI 3.0 link to the PCH chipset. AMD’s AM4 Ryzens have 24 Gen3 lanes, again with four for the chipset—four more are ded­i­cated to the first M.2 NVMe slot. While our graph­ics cards gen­er­ally don’t need a faster PCIe link, es­pe­cially with x16 con­nec­tions, chipsets can run into bot­tle­necks.

Con­sider In­tel’s Z370 chipset, which can sup­port up to 24 PCIe Gen3 links for M.2 slots, USB ports, net­work con­nec­tions, au­dio, and ad­di­tional PCIe slots. All that data still goes through a tiny straw. Most of the time, we don’t hit ev­ery­thing at once, so it’s not a prob­lem, but if you try do­ing RAID 0 with two M.2 SSDs, the chipset link is a lim­it­ing fac­tor, and per­for­mance isn’t much bet­ter than the fastest sin­gle M.2 drives.

M.2 SSDs in gen­eral are an­other area where Gen3 con­nec­tions are a bot­tle­neck. Many NVMe drives can sat­u­rate the in­ter­face, top­ping out at 3.5–3.8GB/s for se­quen­tial trans­fers. With the size of the M.2 con­nec­tor, go­ing to a wider x8 PCIe link isn’t an op­tion—PCIe 4.0 would solve this. USB 3.1 Gen2 is an­other rel­a­tively re­cent tech, but with 10Gb/s per port, it would only take four ports to sat­u­rate the chipset to CPU link.

Graph­ics cards could also ben­e­fit in some work­loads—like ma­chine learn­ing and GPGPU. And even though SLI and Cross­Fire see less use th­ese days, dou­bling the PCIe speed would mean con­sumer sys­tems like LGA1151 and AM4 could pro­vide two x8 Gen4 con­nec­tions that would have the same band­width as x16 Gen3.

I won­der if we might skip Gen4 sup­port. There’s cost in­volved in bring­ing a prod­uct through val­i­da­tion and test­ing, so why test and val­i­date against Gen4, then re­peat the process a year later for Gen5? Then again, if we’ve been OK with Gen3 band­width for seven years, dou­bling it should carry us well into the next decade.

We don’t nec­es­sar­ily need the ex­tra band­width now, but there are sce­nar­ios where it could be use­ful in the fu­ture. Leav­ing it out of cur­rent-gen­er­a­tion moth­er­boards and chipsets means they’re more likely to need an up­date. It also means we’re less likely to see SSDs and graph­ics cards adopt Gen4.

It’s the clas­sic chicken and egg sce­nario, and for now, PCIe 4.0 is solely used in su­per­com­put­ers. But I’m hope­ful that 2019 will change things, and in­crease our chipset link band­width.

While graph­ics cards gen­er­ally don’t need a faster PCIe link, chipsets run into bot­tle­necks.

The PCIe x16 slot hasn’t changed in ap­pear­ance much over the years.

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