PCIe Gen 5 Explained
It seems like it was just yesterday that we were talking about PCIe Gen 4, so to hear that PCIe Gen 5 is not only upon us, but already built into current generation products, well that’s a bit of a surprise. So, what’s the deal with PCIe Gen 5? How fast is it? What even supports it, and why should you care? Well I’m aiming to answer those questions, so stick around!
PCIe straight up doubles its transfer rate every generation – Gen 3 runs at 8GT/s, Gen 4 runs at 16GT/s and Gen 5, you guessed it, runs at 32GT/s. Gigatransfers per second by the way is the theoretical limit, before actually encoding any data. In the real world, that means an x16 slot running at Gen 3 caps at around 16GB/s, run it at Gen 4 and you’ll get 31.5GB/s, and Gen 5 smashes through 63GB/s, which is frankly insane. This improvement comes from a number of changes, primary of which is an insanely fast clock – 32GHz specifically. That’s a pulse every 31.25 PICOSECONDS, and is over 6 times faster than the CPUs that are managing that data. Mental!
Speaking of the CPUs, the platforms that support Gen 5 already exist – well one of them anyway. Intel’s latest Alder Lake CPUs, their 12th gen lineup, and their accompanying Z690 motherboards already support PCIe Gen 5. It’s fairly limited support, with most boards only supporting the top x16 slot, although some boards do also allow the second x16 slot – the one also connected to the CPU which can split the 16 lanes into two sets of 8 – to run at Gen 5 speeds too. No boards I’m aware of support PCIe Gen 5 to any M.2 slots though, meaning the only way to make use of a Gen 5 SSD would be to install a PCIe to M.2 card (that also is rated for Gen 5) in one of the x16 slots.
AMD’s upcoming Zen 4 based Ryzen 7000 series CPUs, and accompanying X670E chipset motherboards will fully support PCIe Gen 5. That means everything from the x16 slots and M.2 slot connected to the CPU directly, the dual-chip chipset and everything connected to it will all be able to run at full Gen 5 speeds. That’s impressive for sure – although interesting the more ‘standard’ X670 chipset will also support Gen 5, but only for “Storage and Graphics”, i.e only the lanes directly connected to the CPU. Finally, their more budget option will also support Gen 5 – but only to the direct-connect M.2 slot, not to the x16 slots or the chipset. That’s so the B650 boards can remain cheaper by not having to build out the very shielded traces and hardware required to communicate that quickly.
Ok, so we have the chicken, what about the egg? What hardware can you actually use with these Gen 5 platforms? Right now your options are pretty sparse. In fact, when it comes to commercially available products, NVIDIA’s datacenter Hopper GH100 GPU is about it. That might cost you a pretty penny though – somewhere around $40,000 – and is very much designed to run in datacenter applications like machine learning training, scientific computation or data analysis and management. Sadly, it’s not a gaming card.
What about storage? Well, Phison demoed their new E26 controller a couple weeks ago which peaked at just under 12.5GB/s on reads and around 10GB/s in writes. Which is just… mind blowing. That sort of performance is literally 4 Gen 3 drives in RAID 0 but from a single drive. And that’s nowhere near the max 4 lanes can offer – we can expect much closer to 16GB/s which is absolutely incredible and more than anyone could need for a long while yet.
Which brings us nicely onto… but why though? If you don’t have anything to do with a datacenter or server farm, PCIe Gen 5 doesn’t matter to you. For enterprise users, being able to double the bandwidth you have to your network, storage and accelerators, that’s a big deal – although even that is going to take a few years for Gen 5 chips, boards and devices to make their way through validation and security revisions before companies actively adopt them. A Gen 5 x16 slot will now be able to run 400Gbps network cards, literally doubling the total bandwidth that cards make use of.
Eventually we will get consumer products that support Gen 5, likely storage first, then graphics cards, and of course more bandwidth is always more better, but realistically it’s likely to be a decade before it’s a necessity. Looking back at PCIe Gen 3 – that’s been in CPUs and motherboards since 2011, but it took until late 2016 for an SSD to come out that could actually make full use of the bandwidth, and for most people that’s still an incredibly fast drive and more than the average user needs. Sure, when the Direct Storage API comes around a fast drive will be real useful, but a full speed Gen 3 drive is still going to perform perfectly well for years to come. Gen 4 was a touch faster in its “full speed” development, but even with Direct Storage that is still likely to be overkill for even gamers for a while yet. Even looking at graphics cards, most GPUs don’t use more bandwidth than a Gen 3 x16 slot can provide – only the most recent, highest end cards have started to exceed that – so if we aren’t even close to needing Gen 4, you really don’t need Gen 5. But it’s cool though.
So, that’s a look at PCIe Gen 5, what supports it, and why you should(n’t) care.
