I’ve recently acquired a Lenovo ThinkStation C20 (4263) system (Intel Tylersburg 5520).
The dual-processor mainboard is equipped with six identical 4 GB RAM-Modules.
The OS w10 pro x64 (10.0.15063.413 (Win10 RS2)) indicates 24 GB of Memory.
AIDA64 indicates 24 GB of Memory in the Memory Tab, but the SPD information lists 12 GB (3 of 6 RAM-modules) only.
May I ask if this is a bug or a feature?