The HP Z420 white RAM slots aren't compatible by themselves.
The HP Z420 white RAM slots aren't compatible by themselves.
I purchased the HP Z420 for roughly $110, assuming I could use my 4x4GB non-ECC DDR3 sticks. I expected them to work since I had those, but none did. I thought the model didn’t support non-ECC DDR3 modules. After switching to my single 8GB registered ECC stick, it worked—only in the black slots. In the white slots, populating out of order caused red lights, a beep, and a memory error. The manual says slots must be filled in sequence, but I managed to do so without order. Anyone familiar with HP Z4xx systems should confirm this? z420_memory_configurations.pdf
The guide instructs to start with the black slots first. Each memory channel includes one black and one white slot. Memory functionality on systems like this can be unpredictable. This is mainly due to testing only the memory type they plan to sell, such as ECC unbuffered. The CPU and chipset handle other formats, leading to inconsistent behavior—some items work while others don’t. The Dell model (T3610) using the same chipset will support everything from standard unbuffered dimms to ECC-registered dimms.
Each white and black slot stands for one channel. With only four working RAM slots, the odds of having all channels functional seem low. The error message you're seeing during boot suggests a memory training issue, possibly related to the test results. It might help to double-check your RAM configuration and ensure everything is properly seated.