I have a desktop at home. The CPU is i5-6400. Internet search shows me the processor can use DDR4-1866/2133 or DDR3L-1333/1600 @1.35V. I opened the case and found there are two slots, both having DDR3L-1333 4GB modules installed (total 8GB, DIMM module).
I learned I can't insert DDR4 modules becaus the slot is not compatible. Of course I could update to two 8GB DDR3L-1333 modules, but can I upgrade the memory with two 8GB DDR3L-1600 modules? (total 16GB, faster memory). Is there any CPU grade for the memory interface speed?