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I've got a D & N MEM-CM9 in my OSI, currently hooked up to a 5.25" floppy drive. I also have an 8" Shugart 901 drive and I'd like to use both with the OSI at the same time. It looks like you have to change the jumpers on the D & N depending on 5.25" or 8" to change the timing so I don't see how it could do both at the same time. Can you add a second floppy controller card?

As no one else has answered this, I'll weigh in.

The short answer is no, you can't have both 5.25" and 8" floppies connected to the same system at the same time. I guess it would be possible to have a second disk interface at a different address (like $C1xx), but since no operating system that I know of supports such a thing, it would be kind of pointless, unless you were going to create (or modify) one yourself to do so.

I think you could put a switch in place of the jumper to set the speed of the disk interface, and then connect one of two paddleboards (A13 ?), but it would still be one at a time. Whether it would be safe to disconnect one and connect the other while power was on (to transfer data in RAM), I don't know. Transferring software or data between the two types of drive was always a problem. I think the usual method was to use an RS-232 connection between two systems. I was once called on to transfer a software package written by novelist Charles Platt from 5.25" to 8", and what I did was load each file into RAM on my C1P, then run a short routine on each end to move it onto my C2-8P and save to 8-inch disk, making appropriate changes where needed.

Edit: With the advent of the Gotek solid-state "floppy drives", it is possible to load an image of an 8" disk into a system configured for 5.25" disks (and I presume vice versa) simply by changing the bit-rate value stored in the header of the disk-image file, so data can be transferred back and forth that way.