Question about XMP and processor specs

[LittleMissMurder]

Hi gang,

I plan on upgrading to a new build soon. I've settled on the i5-13600K, but am at a loss as to which DIMMS to go for. I will likely plop for a DDR-4 setup (because $$$), but this is where the confusion comes in.

The spec sheet on Intel's website lists DDR4-3200 or DDR5-5600 as the supported maximum speeds if 2 dimms are populated. My question is, where does XMP figure in this picture? Assuming the MB supports it, and you can enable an XMP profile for, say, DDR4-4800, is there any point to getting RAM rated for this speed when the rated CPU maximum is DDR4-3200? Will the CPU simply throttle it back to 3200?

I hope this makes sense. Thank you in advance!

 

[Woomack]

I wouldn't go DDR4 because the price difference isn't big nowadays. DDR5 went down much faster than expected.
Probably every Z790/B760 motherboard supports DDR5 at 6400/6800. Most support 6800-7200. Some support 7600 or higher. Above 6800, there is barely any performance gain, but it is safe to get something good at 6400.

DDR4-3200/3600 is supported by every motherboard. If it doesn't, then the motherboard is broken. Probably every motherboard will work at 3600-4000 XMP, even from less popular brands. Most even cheap series should work at 4266-4400 XMP. Some higher series will work at 4800+. However, above 3600, you won't see any significant performance gain.
If the motherboard doesn't pass training at XMP, then it will start at default SPD settings, so usually 2133-2666. Most motherboards won't run at 4800 XMP. Because of the architecture, it's even pointless to waste money on 4800 kits. It's better to go DDR5.

The best if you decide on the motherboard and check QVL, as there are compatible memory kits at XMP settings. You can pick something from the list or something similar (similar main timings and clock).
Again, I recommend DDR5 motherboards as they're usually better (as better quality and with better controllers, but there are exceptions), and you can expect longer support as most brands focus on DDR5 and improvements for higher series. Performance-wise, DDR4 and DDR5 will be almost the same, so if you find a significantly cheaper DDR4 option, then why not.

 

[LittleMissMurder]

I wouldn't go DDR4 because the price difference isn't big nowadays. DDR5 went down much faster than expected.
Probably every Z790/B760 motherboard supports DDR5 at 6400/6800. Most support 6800-7200. Some support 7600 or higher. Above 6800, there is barely any performance gain, but it is safe to get something good at 6400.

DDR4-3200/3600 is supported by every motherboard. If it doesn't, then the motherboard is broken. Probably every motherboard will work at 3600-4000 XMP, even from less popular brands. Most even cheap series should work at 4266-4400 XMP. Some higher series will work at 4800+. However, above 3600, you won't see any significant performance gain.
If the motherboard doesn't pass training at XMP, then it will start at default SPD settings, so usually 2133-2666. Most motherboards won't run at 4800 XMP. Because of the architecture, it's even pointless to waste money on 4800 kits. It's better to go DDR5.

The best if you decide on the motherboard and check QVL, as there are compatible memory kits at XMP settings. You can pick something from the list or something similar (similar main timings and clock).
Again, I recommend DDR5 motherboards as they're usually better (as better quality and with better controllers, but there are exceptions), and you can expect longer support as most brands focus on DDR5 and improvements for higher series. Performance-wise, DDR4 and DDR5 will be almost the same, so if you find a significantly cheaper DDR4 option, then why not.

Thank you for the information. It doesn't directly answer my question but is very useful nonetheless - I read between the lines that XMP ignores the processor's tech specs.

I took a look at this very good video and it suggests that low-latency DDR4 is generally faster that DDR5 because DDR5 runs at 2T. I'm going for a fairly budget build so will go for DDR4 since the prices in my neck of the woods for mobos and ram are much better for DDR4.

 

[Woomack]

Thank you for the information. It doesn't directly answer my question but is very useful nonetheless - I read between the lines that XMP ignores the processor's tech specs.

I answered all your questions but maybe expanded it too much, so it can be confusing.

I guess you mean the manufacturer's specs for the memory controller integrated into the CPU, then you can say that. Both, AMD and Intel, declare much lower maximum supported memory frequency than they can actually handle. Since it's widely tested by the motherboard and memory manufacturers, then depending on the motherboard, the supported maximum frequency is higher.
Another thing is that memory controllers are scaling well only up to some frequency. Scaling like you see significant performance gain, at least in synthetic benchmarks. In games, it's not so visible. The difference between DDR4-2133 and DDR4-3600 is about 5-10% in some games. The difference between DDR4-3600 and 4000+ is typically 1%. The same, difference between DDR5-4800 and DDR5-6400 is 3-7%, anything higher is like 0-1%. If you manually tweak multiple settings, then you will see a better performance at higher clocks, but it's often not worth the time.

I took a look at this very good video and it suggests that low-latency DDR4 is generally faster that DDR5 because DDR5 runs at 2T. I'm going for a fairly budget build so will go for DDR4 since the prices in my neck of the woods for mobos and ram are much better for DDR4.

It's not true. Command Rate gives 0% performance gain on modern platforms (out of synthetic benchmarks). Not to mention that every single XMP profile has 2T/N (DDR4 and DDR5), so you have to set it manually to 1T/N, and you can do it the same way for DDR4 and DDR5.
The optimal DDR4 setting without a hassle is 3600 CL14, better if more, but both AMD and Intel switch to a 1:2 IMC ratio above some point (typically 3733-4000), and then the memory controller and other related things limit the RAM performance. Some applications work better at a higher clock, regardless of this ratio, some work worse.
The most popular DDR4 vs DDR5 performance comparisons were made just after the DDR5 release, and most people around the web repost these conclusions. In short, the conclusions were that DDR4 is still better for games ... but back then, DDR5 was 5200-5600, while now a standard is already 6400, and up to 8200 is available in stores. We also went from 6000-6400 CL40 to 7200 CL34 or 8000 CL38 in about a year.

I'm not saying that your decision about DDR4 is wrong. I just comment on some things. As I said, if the price is significantly lower, then DDR4 is still a good option and often not worse.