One particular server I have, docs say "Supports up to 4GB of RAM". With 4GB of RAM installed, the OS sees 3GB.
Call up SuperMicro support, they say "yeah, the server BIOS/chipset/whatever puts a 1GB memory hole in at 3GB so the OS can only use 3GB."
"So your docs are wrong and it only supports 3GB?"
"No, it supports 4GB."
"…"
Fuckers.