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I'm adding 16 GB of RAM for my Windows 11 Desktop . Motherboard is Asus B550M-A

CPU is AMD Ryzen5950.

Per google Ryzen5950 has a base clock speed of 3.4 GHz and a max boost clock speed of 4.9 GHz.

I'm confused here. I heard that RAM speed may bottleneck CPU speed.

But searching over internet I see RAMs are in MHZ speed. So Assuming I Do Not overclock my system and AMD CPU runs at 3.4GHz, what kind of RAM speed give me max benefits?Assuming I buy PNY brand RAM, should I got for 3200MHZ or 3600MHZ or 4000MHZ?

S Nash
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    CPU and RAM clock rate are unrelated and do entirely different things. – Daniel B Sep 12 '22 at 19:18
  • @Daneil B , so none of these has a "bottleneck" effect on the other one? – S Nash Sep 12 '22 at 19:21
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    @Daneil B So if money was not a factor here, to get my system fastest I should go with the Max RAM speed supported by my motherboard(per manual 4400MHZ)??? – S Nash Sep 12 '22 at 19:23
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    Note that the JEDEC spec for DDR4 only goes up to 3200Mhz, so you will have to use the XMP profiles (easy overclocking) in order to run anything faster at its label speed. https://en.wikipedia.org/wiki/DDR4_SDRAM#JEDEC_standard_DDR4_module – Frank Thomas Sep 12 '22 at 19:31

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RAM can bottleneck CPU or vice versa, but it doesn't mean you have to match the frequencies. It just means that if one is too slow, the other one won't be able to run at its full potential.

Am I reading it correctly that you want to keep your current RAM and add more? If that's the case, ideally you'll want to buy identical modules as already installed in the system, or at least to match the frequency and timings (CL etc.). You can read these parameters from your current modules using CPU-Z or other software.

Why match them rather than buy faster? Because all RAM has to work in sync and faster modules will slow down to match the slowest one. Buying faster RAM makes sense if it's cheaper (it happens sometimes). Buying slower isn't a good idea because it will slow down your current (faster) RAM.

Note that frequency isn't the only factor at play. There's also a bunch of timings, with CL being the most important. The lower the timings, the better. Were you replacing your current RAM (rather than keeping it), you'd generally want to look for the highest frequency to CL ratio, but with frequency no lower than 3000 MHz. For example 4000 MHz CL20 is worse than 3600 MHz CL16 (because 4000÷20=200 and 3600÷16=225).

(And there's more timings than just CL, and with AMD CPUs the Infinity Fabric runs at RAM speed so sometimes higher frequency is better even with worse timings… There's a lot of nuances. If you don't want to dive into this rabbit hole, match your current RAM or buy by highest frequency÷CL)

It's worth keeping in mind that you'll be seeing diminishing returns the higher frequency you get. Also better RAM is significantly more important when you're using the integrated GPU, but that mostly matters in low budget systems of course.

On a side note, assuming that CPU runs at 3.4 GHz is incorrect, because it will by default boost its clocks up to 4.9 GHz, even without any OC. That's how modern CPUs work: 3.4 GHz is the "guaranteed" clock that the CPU can maintain indefinitely, 4.9 GHz is what it can run at for limited period of time as long as it doesn't get too hot and the motherboard is able to provide enough power.

gronostaj
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