Although memory has generally been a set-and-forget kind of deal for years, the arrival of Ryzen CPUs has made the topic worthy of careful consideration again. Ryzen 5 and Ryzen 7 builders need to think carefully about the DDR4 memory they're choosing for their systems. AMD's newest CPUs have a reputation for being picky about the DDR4 RAM they'll play well with, and getting the most out of Ryzen's memory subsystem requires some careful DIMM selection.
AMD places restrictions on the maximum speed at which certain types and certain arrangements of memory can run with an out-of-the-box system based on Ryzen 5 and 7 CPUs. Here's a quick recap of the stock speeds one will get with common memory configurations:
- Dual-channel, dual-rank, four DIMMs: DDR4-1866
- Dual-channel, single-rank, four DIMMs: DDR4-2133
- Dual-channel, dual-rank, two DIMMs: DDR4-2400
- Dual-channel, single-rank, two DIMMs: DDR4-2667
Ryzen Threadripper CPUs are subject to similar limitations, just with four memory channels instead of two:
- Quad-channel, dual-rank, two DIMMs per channel: DDR4-1866
- Quad-channel, single-rank, two DIMMs per channel: DDR4-2133
- Quad-channel, dual-rank, one DIMM per channel: DDR4-2400
- Quad-channel, single-rank, one DIMM per channel: DDR4-2667
If you're trying to get the highest speeds possible from Ryzen's memory controller, a pair of single-rank DIMMs is a must. Before taking Ryzen RAM to its limit, refer to your motherboard's qualified vendor list for compatible RAM (or consult memory vendor documentation) and get ready to do some manual tweaking of voltage and timings if XMP profiles aren't doing the job.
AMD recently rolled its AGESA 126.96.36.199 base firmware for Socket AM4 motherboards out to mobo makers, and firmware updates containing that base code are now widely available. You can get a full sense of what changed in AGESA 188.8.131.52 from the horse's mouth, but the key changes are memory multipliers as high as 40 (good for 4000 MT/s RAM) and command rate choices of 1T or 2T. Our practical experience suggests that 3200 MT/s remains near the upper limit for reasonable RAM timings and voltages on AM4, but AGESA 184.108.40.206 might help make it easier to run kits at those speeds.
Intel's Kaby Lake CPUs and the Z270 platform, in contrast, support most capacities and configurations of DDR4-2400 out of the box without a hitch. We've had fine luck turning on XMP with our Kaby Lake systems and getting stable operation with fast DDR4-3200 memory across a range of kits, as well. Even exotic kits, like the aforementioned DDR4-3866 DIMMs, can be made stable with only a bit of tweaking (assuming XMP doesn't take care of stability to begin with). The payoff for fast RAM starts to diminish around DDR4-3200 with modern systems, but those chasing every last drop of performance won't be disappointed by faster memory.
If you're building an X299 or X399 system, be sure to choose (or assemble) a kit with either four or eight DIMMs to reach the capacity you want. Both Ryzen Threadripper and Skylake-X CPUs need four DIMMs to take full advantage of their quad-channel memory controllers. Intel's X299 platform boasts admirable RAM compatibility. We've run four-channel DDR4-3600 kits in our X299 test bed without issue, though spending huge amounts of money on super-fast RAM for X299 doesn't seem to offer appreciable performance benefits. Just as we'd approach RAM for the Z270 platform, we wouldn't shell out for X299 kits runnning faster than 3200 MT/s unless you have cash to burn.
Whether you're building with an AMD or Intel CPU, there's no reason at all to consider anything but 8GB of memory in an entry-level build these days. It also doesn't cost a whole lot extra to step up to 16GB of RAM any longer. If you use Photoshop or other creative applications in tandem with a lot of open browser tabs, 16GB of RAM is starting to become a baseline, not an upgrade. Even 32GB or 64GB of RAM might not be outlandish for the heaviest multitaskers.
AMD memory kits
|HyperX Fury 8GB (2x4GB) DDR4-2400||$84.99|
|G.Skill Fortis Series 16GB (2x8GB) DDR4-2400||$141.99|
|G.Skill Fortis Series 32GB (2x16GB) DDR4-2400||$277.99|
|G.Skill Flare X 16GB (2x8GB) DDR4-3200||$187.99|
We've pored over spec tables, motherboard manuals, and vendor data sheets to assemble a good range of RAM options for Ryzen builders and budget Intel builders alike. For the most part, though, G.Skill has made that work easy with its Fortis and Flare X kits, which are explicitly designed to work with Ryzen systems across a range of capacities and speeds. If you don't want to pore over QVLs for hours, those G.Skill kits should take out a lot of the guesswork for Ryzen RAM.
Intel memory kits
|G.Skill Aegis 8GB (2x4GB) DDR4-2400||$74.99|
|G.Skill Ripjaws V 16GB (2x8GB) DDR4-3200||$153.99|
|G.Skill Aegis 32GB (2x16GB) DDR4-2400||$275.99|
|G.Skill Trident Z 32GB (2x16GB) DDR4-3200||$303.99|
|G.Skill Trident Z 64GB (4x16GB) DDR4-3200||$612.99|
Intel's official spec for Kaby Lake-compatible DDR4 RAM is DDR4-2400 running at 1.2V, but we've used significantly faster DIMMs like DDR4-3866 in our CPU and motherboard test rigs without issue. In our review of the Core i7-7700K, we found that speedy RAM might offer performance benefits in specific scenarios. With that in mind, and the fact that DDR4-3000 and DDR4-3200 kits can be found for prices close to their DDR-2400 counterparts, we see little reason not to go with a faster kit unless your motherboard isn't based on a Z170 or Z270 chipset.
If you're building an X299 or X399 system, be sure to choose (or assemble) a kit with four or eight DIMMs to reach the capacity you want. Intel Skylake-X and Ryzen Threadripper CPUs need at least four DIMMs to take full advantage of their quad-channel memory controllers. Although the stock RAM speed for either type of rig is 2666 MT/s (save for the Core i7-7800X at 2400 MT/s), we used high-speed DIMMs in our review of those CPUs without a hitch.