If you don't touch your BIOS then most, if not all, of your settings are defaulted to "AUTO". That means that the values can fluctuate as needed and the end result can be instability in your system. When I say "hard-set" I mean manually entering in the values so that they will not fluctuate but rather run at a specified value, whether it be the frequency/voltage/timing.
For your RAM, you should read the sticker that is physically on the side of the RAM stick. It should state the timings/voltage/frequency right on that sticker. Those values are what you should manually set within your BIOS as those are the rated specifications for your specific RAM sticks.
So, as an example, if your RAM sticks state 1333Mhz, 8-8-8-24 2T 1.65v, then you need to enter in those specific values in your BIOS.
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