I will cover just the two most usual hardware configurations: (a) BA23 box - 1st RD53 is DS3, 2nd RD53 is DS4 (a 6 button front panel is required or you can build your own) - never had to change anything on the RX50 when ONLY a single dual RX50 is used (b) BA123 box - 1st RD53 is DS3, 2nd RD53 is DS3 (they are the SAME and special BA123 READ ONLY switches are required) - never had to change anything on the RX50 when ONLY a single dual RX50 is used I set up a MINC system with an RD53 once - don't ask! The jumper was DS3. By the way, the RD53 is just a Micropolis 1335 (if I remember correctly) with R7 set as a zero ohm resistor so the RQDX2 and RQDX3 recognize the extra circuit. The above jumpers apply to all RD51, RD51, RD53 and RD54 drives with the RQDX1, RQDX2 and RQDX3 controllers. The RD53 can't be used with the RQDX1 and the RD54 requires the RQDX3. With the BA123 box, there is a special distribution panel (13th slot) for the hard drives and the floppies. If you don't have enough information, please ask. All of the above is from memory - there may be some mistakes! Did this help? If you make the mistake of having both RD5n drives as DS3 with the BA23 box when the drives are not WRITE PROTECTED, you will destroy the Low Level Format. I find it is impossible to forget that situation - you only need to do it ONCE!!!!!!!!!!!!!!!!!!!!!!!!! Jerome Fine