Gigabyte GA-6OXC User Manual page 71

Memory
The category is display-only which is determined by POST (Power On Self Test) of the BIOS.
Base Memory
The POST of the BIOS will determine the amount of base (or conventional)
memory installed in the system.
The value of the base memory is typically 512 K for systems with 512 K memory
installed on the motherboard, or 640 K for systems with 640 K or more memory
installed on the motherboard.
Extended Memory
The BIOS determines how much extended memory is present during the POST.
This is the amount of memory located above 1 MB in the CPU's memory address
map.
64
BIOS Setup