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Which desktop PC will perform better? One with 32GB 2133Mhz RAM or 16 GB 3200Mhz RAM assuming that applications do not use more than 10GB RAM?

Assume that the CPU used is AMD Ryzen 7 2700x. The motherboard used is B450 Aorus Pro Wifi from Gigabyte.

Given the CPU you are looking at, it seems likely the 16GB 3200Mhz would create the faster system.

However it is worth pointing out that the Motherboard is also an important part of this equation. It is the combination of the RAM, CPU and motherboard together that will determine the speed 'cap' your RAM will function at. Do you know what motherboard will be used in the system?

A good rule of thumb when choosing RAM for the fastest performance possible is, in this order:

1. Have ENOUGH memory for your needs. I can't stress this enough, this
   is the most important parameter. Paging is various orders of
   magnitude slower than just reading/writing to RAM, even lacking a
   small amount of RAM can have a considerable impact on performance. In your case,
   since you state that you won't likely need more than 10GiB,
   upgrading from 16 to 32GiB will have close to no effect. But the opposite case if the most penalizing, no matter how fast is your RAM if it cannot hold all the data it should.



2. Use dual (tri/quad) channel if possible: Bandwidth is doubled (tripled/quadrupled) under optimal circumstances, and usually there are few reasons to not pair modules when possible.




3. Get the highest frequency AND lowest latency memory you can/want
   to afford. A very high frequency RAM with really bad latencies can perform worse than a slow ram with tight latencies. On Ryzen usually frequency has a bigger impact since
   infinity fabric runs syncronously to the RAM, and overall processor
   performance is sightly improved, but not at any cost. Note that,
   specially on early bioses, some memory IC's were problematic,
   specially if you want 3200+. Nowadays its less likely to happen, but
   if you want to oc seriously or want to push the limits of your
   platform, aim for ram using samsung B-die (more expensive, higher
   frequencies usually). If you are not into that, doesn't matter a lot, but make sure to check QVL for your motherboard, just in case.

Having that in mind, the answer to your question is obvious, specially on Ryzen, but virtually on any case: 16GiB@3200Mhz will perform better than 32GiB@2133, given no weird latencies are used in the first case. Be aware that for a user that does high-resolution photo editing, for example, 32gb at 2133mhz will likely be the best setup.