ECC vs non-ECC DDR5: Don't mix them—pick one type and stick with it

Mixing ECC and non-ECC DDR5 modules usually results in a no-boot or random crashes because they use different signaling and parity logic. Most consumer boards refuse to POST with mismatched modules, and even server boards that accept both treat the whole system as non-ECC, wasting the error correction benefit. DDR5’s on-die ECC is for internal data integrity, not system-level correction—actual registered or unbuffered ECC modules are different. If you need ECC, buy a matched set; otherwise, save money and go plain DDR5.