Officially, standard desktop DDR4 tops out at 3200MHz. Unofficially, RAM manufacturers have pushed the JEDEC standard to much higher clocks. Corsair, however, has gone for broke with a new DDR4 kit that can break the 5GHz barrier when paired with an X570 motherboard. Corsair has certified multiple MSI boards — the MEG X570 Godlike, X570 Ace, X570 Unify, and Prestige X570 Creation — to use its new LPX Vengeance RAM, clocked at an eye-watering 5GHz. There’s an optional fan you can hook up to the kit to make sure the air flowing over the RAM modules is enough to keep them cool.
Running your DDR4 at 5GHz has a price, however — and that price is an eye-watering $1079 for a kit of 16GB RAM. 16GB of DDR4-4000, just to put this in perspective, is currently running $116. You’re paying more than 10x the cost for a 1.25x increase in RAM throughput. And while these new sticks of RAM definitely offer more clock rate than anything we’ve ever seen, getting this much speed out of an AMD CPU requires you to run the Infinity Fabric at a much lower clock.
In order to support skyscraper RAM clocks, AMD made changes to how the 7nm Ryzen 3000 family handles the Infinity Fabric clock. Ordinarily, RAM and IF are clocked identically. This holds true, so long as your RAM clock is set to DDR4-3733 or below. At DDR4-3733, Ryzen 7nm CPUs use a 1:1 Infinity Fabric multiplier. Above this speed, they drop to a 2:1 modifier. This has the side effect of significantly increasing memory latency.
AMD’s graph suggests that a 1.14x increase in RAM clock (from 3866 to 4400MHz) leads to a 7 percent reduction in memory latency. According to Corsair, memory timings on this RAM are 18-26-26-46, which at least corresponds to the CL18 RAM AMD was using for its DDR4-4400 test. If we extrapolate out the results, we would expect DDR4-5000 to improve RAM latency by another 7 percent compared to the 75ns measured for DDR4-4400CL18. That would suggest roughly 70-71ns of latency, which isn’t quite as good as the measured 69ns of latency for DDR4-3200.
This type of RAM may be used by overclockers going for benchmark records, but the one product that could use it the most — namely an APU — doesn’t currently support clocks this high. AMD’s Ryzen 7 3000 APUs are based on 12nm silicon, not 7nm, and no one would ever put $1000 worth of RAM in a system with an integrated GPU to make it faster. This sort of mismatch between the cost of the DRAM necessary to wring top performance out of an APU and the value of putting that RAM in an APU-powered system is why enthusiasts have hoped that AMD would come out with an HBM-equipped chip at a reasonable price. So far, prices on HBM haven’t been reasonable enough to allow that to happen.
The truth is, the price of this RAM is too high to justify it for anything but record-breaking bragging rights. Even in a scenario where a Ryzen 9 3950X would benefit from DDR4-5000 as opposed to DDR4-3200, thanks to having 16 cores on two memory channels, it would ultimately make more sense to buy a Threadripper rig with the money you’d save on this memory. But as an intrinsic demonstration of achievement, separate from any question of usefulness? Hitting 5GHz on DDR4 is a heck of a record. Well done, as far as that goes.
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