[pibil1]

Greetings and happy new 2021

I have a x79 motherboard with a Xeon E5-2640 actually with 4x4gb of DDR3 ECC Ram. I'm thinking about upgrading the ram to 32 Gb, is it mandatory to buy the exact same Ram modules in order to keep Quad Channel activated or once I have 4x4Gb already ensures Quad Channel support regardless what I upgrade?

Thank you in advance,
Kind regards

[flotus1]

So your particular "X79" motherboard has 8 DIMM slots, and is actually capable of quad-channel operation? Asking because some of those popular "X79" boards from chinese vendors only have 4 DIMM slots, and some of them do not support quad-channel operation.

Assuming the answer to both questions is yes:
With ECC (RDIMM? please clarify) memory, it is pretty straightforward. As long as you have the same amount of memory installed in each channel, quad-channel should work. Consult the manual for your motherboard if you want to install DIMMs with different capacity or number of ranks. It might hint at some preferences for the exact order of DIMMs.
Other than that, you might want to check how many ranks your current memory modules have. With ECC RDIMM, that info is right on the sticker: 1R indicates a single rank, 2R two ranks. Buy the same for optimal compatibility and performance. And of course, try to match the rated transfer rate and latency as closely as possible for the highest chance of compatibility.
With ECC UDIMM, you might need some diagnostic tools (mostly available for Windows) to find that information.

tl;dr: you generally don't have to buy the exact same DIMMs if you follow some rules for compatibility.