Got it running with 4800MT/s and literally 30 minute boot times in an AM5 machine. The 30 minute boot time could be worked around by enabling the (off-by-default) memory context restore option in BIOS, but it really made me think something was broken and it wasn't until I found other people talking about 30 minute boot times that I stopped debugging and just let it sit for an eternity.
It's so bad. I don't get why they sell AM5 motherboards with 4 RAM slots.
At least that system has been running well for like two years. But had I known that the situation is so much more dire than with DDR4, I would've just gotten the same amount of RAM in two sticks rather than four.
I’m in the same situation! My machine will take 2-5 minute to post every few reboots, it seems random. The messed up part is the marketing material says this things can handle 256gb of ram or whatever absurd number, f me for thinking then 128gb should be no problem. Honestly this whole thing has soured me on AMD. Yea they have bigger numbers than intel but at what cost, stability?
It's the RAM. It needs to "trained" which takes some time but for for some reason these boards seem to randomly forget their training, requiring it to happen again.
I've never had memory training be forgotten with my AM4 nor LPDDR5-based laptops and NUCs. Is this a new thing with AM5 or something? Or just a certain brand of BIOSes?
It's a common issue on consumer boards with DDR5 and more than two DIMMs installed.
Doesn’t affect soldered memory or lower speed memory (like DDR4). Many memory controllers fail to achieve good speeds and timings at all on 4 DDR5 DIMMs, and fall back to running DDR5 at 3600MHz instead.
Ok, so user selects too-high speed, controller tries for ages and fails, but doesn't save since it's overridden by user in BIOS?
I distinctly recall thinking my LPDDR5 NUCs were broken since they seemingly didn't boot the first time, until I recalled the training stuff. Took up to 15 minute on one of them. But neither has had any issues since, hence my question.
DDR5 is much, much more fickle than DDR4 and earlier standards. I think it's primarily due to pushing clock speeds (6000 MT/s would be insanely fast for DDR4, but kinda slow for DDR5).
Memory training has always been a thing: during boot, your PC runs tests to work out what slight changes between signals and stuff it needs to adapt to the specific requirements of your particular hardware. With DDR4 and earlier, that was really fast because the timings were so relatively loose. With DDR5, it can be really slow because the timings are so tight.
You need to enable MCR (which trains the memory once and caches the result for (iirc) 30 days) otherwise yeah, booting is horribly slow, even the 64GB I have can take several minutes but with MCR it boots basically instantly.
Memory training seems to be getting faster with each bios update. In 2024 when I upgraded to AM5, 64GB memory training took like 15 minutes. Now the same setup takes about a minute when it needs to retrain, then near instant with MCR (Windows 11 takes significantly longer to load than the POST process).
It's so bad. I don't get why they sell AM5 motherboards with 4 RAM slots.
At least that system has been running well for like two years. But had I known that the situation is so much more dire than with DDR4, I would've just gotten the same amount of RAM in two sticks rather than four.