I recently bought a Intel S1200BTS + Core i3 - 2100 + 4x4Gb Kingston mem. Inside BIOS it shows 16384 Mb of memory but on the ESXi 5.0 boot spash screen it reports 15,7 Gb and in the vSphere client on the summary screen it shows 16108,09 Mb. Where is the rest of my memory? I know tha BIOS uses 10-20Mb. AFAIK onboard video doesnt take memory from the main RAM. I´m on latest BIOS and tried different options inside it. Thanks!
Different option ROMs use small amounts, here and there. Unless it's off by a few Gb, it's nothing to worry about.