After months of waiting, the well known memconf utility now support x86 systems. Try it yourself!

Here is the output on my personal Sun Ultra 20 workstation (an AMD Opteron machine) running build 51 of OpenSolaris:

# memconf
hostname: unic.thilelli.net
Sun Ultra 20 Workstation (Solaris x86 machine)
Type    Status Set Device Locator      Bank Locator
------- ------ --- ------------------- --------------------
unknown in use 0   A0                  Bank0/1
unknown in use 0   A1                  Bank2/3
unknown in use 0   A2                  Bank4/5
unknown in use 0   A3                  Bank6/7
total memory = 2047MB (1.9990234375GB)