AMD’s RyZen and RyZen third generation (Zen2) CPUs have rewritten the conventional wisdom around computer processors, the one that goes “Intel is the performance and innovation leader, and AMD follows behind with lower performance chips for the budget market”. The RyZen 3xxx processors are beating Intel in the market, with advanced process manufacturing and high performance, while still maintaining their value proposition.
The other script that needs revising is this one “Computer CPUs are not particularly sensitive to RAM memory speed, over-clocking RAM is a frill that results in marginal performance gains”
Well, the AMD RyZen architecture is built to take advantage of memory speed, and increasing the speed of the DDR4 memory in these machines does make an appreciable difference in the performance of the computer overall.
The basic DDR4 memory speed has settled out at 2400 MHz There are choices at 2666 MHz, 2933 MHz, 3000 MHz, 3200 MHz and other more expensive models up to 4400 MHz.
Digression: to be more accurate, DDR4-2400 has a 1200 MHz memory bus speed which at Double Data Rates (DDR) of two operations per clock tick translates to 2400 million transactions per second (MT/s), but lets now ignore that and return to the MHz labeling that everybody uses)
Setting the speed and timings for RAM in your machine is not necessarily automatic. You can buy expensive RAM rated for fast speeds, plunk it in and assume you’re going to get better performance, only to have your motherboard decide to run it at the standard 2133 or 2400 MHz. So to get the most out of your memory, you have to dive into your motherboard’s BIOS settings and make the changes, then test, then test again. Every motherboard and BIOS is going to be a bit different. Every RAM kit will come with some basic values programmed in, but not necessarily the fastest ones. And every motherboard-RAM combination will be stable up to a certain speed, and unreliable above that.
The main features are the Frequency (MHz or MT/s) and the Latency, There are many Latency parameters, the main one that is used for RAM marketing is the CAS latency, which in DDR4 could be anywhere from CL12 to CL19 (with latency, the lower the number the better). In general, as the MHz speed goes up, the CAS Latency also goes up and the price goes up. Your goal is to find the ‘sweet spot’ between high MHz, low latency and affordable price.
For RyZen processors, the sweet spot at the moment seems to be sitting around 3200 MHz and CAS Latency 16. This may change over time as yields of higher performance, smaller process DRAM chips become available.
Single Rank memory modules are easier to overclock than dual rank modules, but that means staying with 8 GB modules (as it is harder to build single rank 16 GB and above modules). That means a limit of 16 or 32 GB memory if your motherboard has 2 slots or 4 slots, respectively. You’ll have to decide if expandability to more than 32 GB is more important than ultimate speed. As always, check the memory compatibility charts for your particular motherboard, and follow the manufacturers guidance for Ranks, capacity and installation order.
The ratings on modules that you purchase are the memory manufacturers claims of how high a speed that they will support on the modules. You may be able to overclock the modules above the top rated speed, and conversely, some motherboard and memory combinations will not be able to reach the rated speed stably. Also note that many higher performance modules require that the voltage of the memory bus be increased beyond the 1.2V standard to 1.35V (over standard but generally acceptable) or even 1.5 V (not recommended) in order to reach the highest rated speeds. Excessive voltage increase creates higher heat and can lead to premature component breakdown.
Here is a link that covers the basics of setting RAM frequencies and latency.
And here is a DRAM calculator for RyZen chips that takes some of the guesswork out.
And if you want a deep, deep dive into the specifics,