install OpenBSD 5.1 snapshot
reinstall OpenBSD 5.0 release in the same machine
then
#dmesg output
OpenBSD 5.1 (GENERIC.MP) #207: Sun Feb 12 09:42:14 MST 2012
dera...@amd64.openbsd.org:/usr/src/sys/arch/amd64/compile/GENERIC.MP
RTC BIOS diagnostic error 11<memory_size>
real mem = 4157599744 (3964MB)
avail mem = 4032761856 (3845MB)
mainbus0 at root
bios0 at mainbus0: SMBIOS rev. 2.5 @ 0xf0450 (82 entries)
bios0: vendor Dell Inc. version "A12" date 12/09/2011
bios0: Dell Inc. OptiPlex 780
...
# sysctl -n kern.version output
OpenBSD 5.0 (GENERIC.MP) #63: Wed Aug 17 10:14:30 MDT 2011
dera...@amd64.openbsd.org:/usr/src/sys/arch/amd64/compile/GENERIC.MP
