Check your board, but yes—ECC UDIMMs will work with a Ryzen 5 5600X on B550.

Yes, you can use ECC UDIMMs with that CPU. The Ryzen 5 5600X has an integrated memory controller that supports unbuffered ECC (non-registered). The catch is the motherboard. B550 chipsets can support ECC, but it’s up to each manufacturer to enable it in the BIOS. Some boards do, some don’t, and even if they do, it might not be advertised.

You don’t need a different CPU. A Ryzen PRO or Threadripper isn’t required for ECC UDIMMs—consumer Ryzen works, but the validation is looser. Check your specific B550 board’s QVL list or manual. If it lists ECC UDIMMs, you’re golden. If not, you might still get lucky, but no guarantees.

If you need guaranteed ECC support, look for a board that explicitly says “ECC support” in its specs—usually ASRock’s higher-end B550 boards or some Gigabyte models. Otherwise, just try it; the worst that happens is it doesn’t detect ECC and runs as non-ECC.

Don’t buy registered or LRDIMMs—those won’t work at all.