8" drive variations

[Tony Duell]

> 
> 
> As hinted at in another post a few days ago, I'd like to add an 8" drive (or 
> possibly more than one if necessary) to my Imagedisk machine in order to be 
> able to archive 8" media.
> 
> My knowledge of 8" drives is practically non-existent, so what are the gotchas 
>   involved? Things like:
> 
> Do 8" drives exist in both hard and soft sector variants? Is one far more 
> common than the other (as with 5.25")?

YEs, but it's not a big problem. The hard sectored drives include a 
little circuit to separate the index and sector pulses, it can normally 
be 'jumpered out'. 

> 
> Do 8" drives exist with wildly different track counts (40, 77, 80 etc.) and 
> again is any one particular flavour far more common than the others?

All common 8" drives are 77 cylinder. I can well believe others were 
made, but I've yet to see one.

> 
> Are there any problems with some particular drives that'll make interfacing 
> them to a '765 type FDC more difficult?

The biggest problem (and it only applies to writing) is the TG43 signal. 
This is s signal that is Asserted _by the controller_ when the head is 
closse to the spidnle that cylinder 43 (The name is Track Greater than 
43, of course). It's used to reduce the write current.

A few drives generate it internally. There have been various solutioned 
mentioned here (using a PIC to count step pulses, etc, for exampe) to 
generate it. 

-tony