HP ProOne 400 G1 All-in-One Hardware Reference Manual page 24

In addition, the computer supports:
●
1-Gbit, 2-Gbit, and 4-Gbit non-ECC memory technologies
●
single-sided and double-sided SODIMMS
●
SODIMMs constructed with x8 and x16 SDRAMs; SODIMMs constructed with x4 SDRAMs are
not supported
NOTE: The system will not operate properly if you install unsupported SODIMM memory.
HP offers upgrade memory for this computer and advises that the consumer purchase it to avoid
compatibility issues with unsupported third-party memory.
18 Chapter 2 Hardware repair and upgrade