[Coco] 720kb Diskettes

[Gene Heskett]

On Sunday 28 February 2016 21:45:58 Theodore (Alex) Evans wrote:

> On 02/28/2016 03:21 AM, Gene Heskett wrote:
> > If those are 5.25" disks formatted in a 96 tpi drive, this is
> > correct, If they are 3.5" DD 720k diskettes, this is an error in the
> > disk formatting.  No 3.5" DD diskette should have a dns=3.
>
> Yes, we should insist on images of 3.5" and 5.25" 720k disks that are
> otherwise identical being incompatible!  After all, who knows when we
> are going to start using 270 tpi 3.5" disks under OS-9.  This notion
> has caused a great deal of grief over the years.

Sarcasm isn't quite the correct reaction Alex.

When dealing with an IMAGE file of a diskette, I am at a loss to 
recommend a std setting, primarily because that image is not going to 
pass thru rb1776, the floppy driver.  This holds true even if, for 
backup purposes, you play with the device descripters wpc and ofs values 
so that the /s1 descriptor is pointing at the floppy image on the HD, a 
trick I have done on several occasions prior to drivewire to gain access 
to a .dsk I just spent a couple hours moving over the /t2 port at 4800 
baud with a 256 byte window, the only way I can keep this machine from 
over running the coco's rzsz 3.3.6 zmodem.

Fortunately we DO have a tool to help us sort it, its called dmode, and 
it can work on one of those images thats wrong by having a dns=3 set, 
because we can do a dmode -filename dns=1 and fix the file itself before 
we write it to an actual floppy.

The - sign prepended to the filename of the .dsk turns dmode into a file 
manipulator, works just fine.

This generally doesn't mean squat in the real world until that image is 
written to a real floppy.  So check that as above and make sure that if 
it is going to be written to a 720k 5.25" 96 tpi disk, that it is set 
for 3, but if its going to be written to a 3.5" DD diskette, it should 
be a 1 because that drive has only one track density.  I also don't 
think it means anything when the .dsk is mounted to one of the /xn 
descriptors as that does not to my knowledge pass thru the rb1776.dr 
floppy driver module.

The minutia of floppy disks, and the mix-n-match involved, is enough to 
drive one to drink...

Cheers, Gene Heskett
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