Panasonic FDD number decode?

[Tony Duell]

> 
> Has anyone information on decoding the model number suffix on a Panasonic 
> 3.5" floppy drive? The number is JU-257-14PF.
> 
> I was told it was a 720K drive when I bought it some time ago but it seems 
> to act like a 1.44MB unit. Need to confirm as I want a 720K for an 
> industrial OS-9/68K system I'm thinking of dragging out of storage. 
> Controller only talks 720K. Controllers in PC's use connector pin two, 
> IIRC, to select lo/hi density. Is my drive selectable by internal jumpers 

On an HD 3.5" drive the only difference between HD and DD operation 
(IIRC) is the write current (higher for the higher coercivity HD media). 
The motor speed, head position, etc are the same in both cases. Maybe the 
read amplifier gets tweaked too..

Most drives that I've seen use the HD-holr-detect switch to set the write 
current. They _may_ also tell the contorller what sort of disk it is 
installed (in other words the disk-type signal is likely to be an output 
from the drive). 

And therefore most HD 3.5" drives work find as DD (720K) ones if given DD 
media.

-tony