Other disk and drive types (Was: Hard-sector discs -- how many

IIRC Western Digial made disk controller chips with normal and inverted data buses (that was, IIRC, the difference between a 1791 nad a 1793, for example). And Intertec (?) used an inverted-bus one without an external inverting bus buffer.... Only on the directory cylinder of Model 1 TRS-DOS and clones AFAIK. When they went to double density, the had to sue standard DAMs since that's all the 179x chips could do. ANd IIRC LDOS used standard DAMs even on Model 1 single-density systems. Soeheter I have an Epson drive unit. It looks a it like the well-knwon TF20, but it isn't. It's something like a BM5. The host interface is a custom parallel one (possibly to a card that pluged into a QX10 or something). The internal controller board contains a Z80A and a _hard disk_ controller chip, the interface to the 5.25" drive is a 34 wasy and a 20 way ribbon cable. Yes, it's ST412 or similar. I have no idea what sort of floppies it uses. -tony