What is an Epson BM5?

Can anyone tell me anything about the Epson BM5 floppy drive unit? Perhaps a little description will help. Physcially it's about the size of an Epson TF20 and has one vertically-mounted half-height floppy drive on the front, along with a power LED. On the back are the usual mains connector and switch and a DB25 socket. The unit splits into 3 main sections, PUS, controller and drive The PSU consists of a mains transformer and a PCB cotnaining an STK7561 hybrid chip. It claims to give out 5V at 2A and 12V at 3A. I guess there's nothing to add about that. The controller claims to be a 'Rabbit Board'. The main chips are a Z80A, 24K of SRAM, 8K of EPROM, an 8237 DMA chip and a 7261, which seems to be a _hard_ drive controller. And of course a lot of TTL glue. The DB25 socket is fixed to this board, it's clearly a TTL level parallel intefave, possibly SCSI-like. The drive links to the cotnroller by a pair of ribbon cables, 1 20 way and 1 34 way. I'm seriously suspecting an ST506/ST412 interface -- yes, on a floppy drive. The drive is Hitachi FDD541. The mechancial side looks conventional, a stepper motor postiioned (it desont _seem_ to be servo-trackedm, although I guess it could micro-step). Spindle motor, etc seem normal to, there is a head-load solenoid. The disks are clearly of the normal 5.25" form factor, but I suspect of a much higher coercivity. There's a logic board fixed to the drive, full of ICs I've never heard off, including a 637B01X0P (Microcontroller?), and an ASIC in a PGA opackage). The contorller interface really does look like ST506/412. Anyone got any ideas? What was it used with, what is the host interface? -tony