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

[Tony Duell]

> Some formats, such as Intertec Superbrain had the data bits inverted
> relative to the header bits

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....

> Some, such as TRS80, got weird with their Data Address Marks

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.

> . . . and then, there are some obscure ones, and even some unusual ones.

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