OK, I think I get it now, but let me check- Another way to say it is that of the 3 slots within a bank:
-Thou shalt not use only 1 slot (troubleshooting mode only)
-2 matching DIMMs are acceptable.
-3 matching DIMMs are also acceptable
And whatever you do within a bank, thou shalt replicate for the same bank on the other lane.
Yes?
Which boils down to if you want to add RAM, you're buying at either 4 DIMMs, or 6.
Looks like I'm OK with the BIOS minimum:
# dmidecode --type 0
# dmidecode 2.10
SMBIOS 2.6 present.
Handle 0x0000, DMI type 0, 24 bytes
BIOS Information
Vendor: Dell Inc.
Version: 2.1.9
Release Date: 05/21/2010
and on the second server
dmidecode --type 0
# dmidecode 2.10
SMBIOS 2.6 present.
Handle 0x0000, DMI type 0, 24 bytes
BIOS Information
Vendor: Dell Inc.
Version: 6.0.7
Release Date: 08/18/2011
Although I have to say the greatly different BIOS versions surprise me a bit. They have different purchase dates, but that's a lot of revisions between 2.1.9 and 6.0.7.