Tiebreaker, as you found out, systems might work with non-ECC memory. Mixing ECC and non-ECC will probably cause all the memory to work in an non-ECC mode.
ECC memory is nice since it automatically corrects single bit errors, and prevents system crashes.
If you're curious how well the Z400 is working with non-ECC memory, you could see if there are any hardware errors in the Windows logs.
- Launch Computer Management (one way to launch is to right click on "My Computer" and click Manage).
- Then go to Event Viewer -> Windows Logs -> System
- Under Actions in the right-hand column, clik on "Filter Current log..."
- In the Filter Current Log popup window, select Critical, Warning, Verbose, and Error in the Event Level selections, and click OK.
You may see a lot of items. Click on the Source header to group the same items together. If there are some WHEA errors, they could be caused by memory errors, either corrected or uncorrected. Look at the description of each error.
Let me know if you see these WHEA errors, I am curious what you find. If there are none, great.