I'm not certain of the mechanics involved, but, you shouldn't be able to trash the format of either drive, unless the Drive Select jumpers are set incorrectly. The only thing that might have an impact on this would be if you try it in a BA23 with an un-modified 4-button front panel. *Maybe* the fact that the Ready/Write Protect lines for the 2nd drive are left floating, is somehow confusing the RQDXn controller, but that seems doubtful. Those lines merely report status of the 2nd drive. The Drive Select and Head Select lines don't go anywhere near the front panel, and there are separate signal lines for drives 0, 1, 2, and 3. required to the disk drive distribution panel; all of the signal lines are there, and ready to use for 2 drives. DEC sold the "upgrade" kit for 2 hard drives; it's called the BA23-UC. It consists only of a 6-button panel. This is the same 6-button panel that was shipped with later models of the MicroVax, which clearly supported 2 internal RD-series disk drives. All the 6-button panels did was to add the extra ready/write protect buttons. There is no extra logic involved. The Write Protect LIGHTS for the RX50's were deleted, as the newer RQDX3 controller doesn't provide any outputs for the floppy write protect lights. Most of this information is documented on-line, in the document "third-party disks.txt". All that need be done to the 4-button panels is to solder 2 resistors onto the boards, to pull the 2 signal lines to their appropriate logic levels. The RQDX3 only uses these signals to establish that the drive is on-line, and write-enabled. It has nothing to do which drive is selected when it goes to write. Have I trashed the format of a drive in a 2-drive BA23 configuration? Yes, I have. But only because I wasn't paying attention, and didn't set the Drive Select jumpers to "3" on both drives. Remember: The distribution panel shifts the signal lines around, and all hard drives need to be set to "3". This could easily trip you up if you weren't paying attention, as some of the drives had DS markings of 0 - 3, and some were marked 1 - 4 . . . Thus, depending on what DS settings you have, you could in theory have 2 drives responding to the same drive select signal, which could trash your format. T