Can I mix ECC and non-ECC RAM in a Dell T1700?

No. You cannot mix ECC and non-ECC RAM in a Dell T1700 — the motherboard expects one type, and mixing usually causes no boot, crashes, or the system treating all sticks as non-ECC. The T1700 supports ECC only if all slots are populated with ECC sticks. For 16GB, buy two matching 8GB ECC or non-ECC sticks instead.