I recently purchased a new (old stock) HP EliteDesk 705 G1 SFF. It came installed with a total of 8GB of RAM (2 sticks of 4GB each, DDR3L) ... I bought 16GB of additional RAM (2 sticks of 8GB each, DDR3), with the idea of upping it to a total of 24GB of RAM.
I installed the two new 8GB sticks into the two empty slots and the BIOS recognized 12GB (one of the 8GB sticks, one 4GB stick)! I rearranged the sticks in every possible way & combination in the four slots and sometimes only 8GB would be recognized, sometimes 12GB, sometimes 16GB, but never all 24GB.
I know that all four sticks of RAM are operational, and that the ones I purchased conform to what the owner's manual specifies and requires (CAS, latency, speed, etc.) - G.Skill's Value 16GB (2x8GB) 240-pin DDR3-1600 SDRAM (PC3 12800), model F3-1600C11D-16GNT. The BIOS was updated to the latest version available from HP's site - version 2.28 Rev A (L06) from March 7, 2017. The CMOS was also reset without change.
When I go into Windows (7 Pro x64), it reports that it sees 23,536MB of RAM! The CPU-Z utility also sees all four sticks of installed RAM too. It's only the BIOS that reports only 12GB (two slots filled, two slots empty).
Is this a problem with the BIOS that HP needs to fix, or a problem with my specific systemboard? Am I really operating with 24GB of RAM in Windows, or just the 12GB which the BIOS reports?