[Coco] Another Coco Virtual Disk Util

[Wayne Campbell]

You are correct, Robert. That byte in all of my vhd images is 3. EmuDisk
does not let me edit it. Format just keeps a hourglass mouse pointer on the
screen and never reports anything. Drag/drop did the same. It never
reported anything.

Wayne
 On Oct 18, 2013 11:39 AM, "Robert Gault" <robert.gault at att.net> wrote:

> Walt Zydhek wrote:
>
>> Are you saying that ALL VHD's should be one head regardless of what DD.FMT
>> reports? That would be an easy fix, and I can force it to always use $82
>> for
>> DD.FMT if it's a VHD if that would be the proper use.
>>
>> -Walt Zydhek
>>
>
> Keeping in mind that this refers ONLY to .vhd emulated hard drives, yes
> the assumption is that there is just one head. More to the point, DD.FMT
> can't say much of anything about hard drives as it is limited to one or two
> heads while real hard drives can have more than that.
> DD.FMT most likely is a holdover from floppy drives where the choice is
> only one or two heads.
>
> The problem is determining if the emulated disk is a floppy or a hard
> drive. The only indicator in LSN0 is the highest bit of DD.FMT and that
> does not help if there is no OS-9 section on the .vhd. For safety, we
> really should always use .vhd if the drive is hard but that has not been
> done consistently.
>
> There is also a problem determining where the "Disk Basic" (ie. 35 track
> drives) start on a .vhd image. The original specs had the .vhd image
> partitioned at $5A000 bytes regardless of whether the first partition was
> formatted for OS-9 or not.
> This spec also required the RGBDOS ROM to contain this offset value of
> $5A000 and that is what determines where RGBDOS starts reading the .vhd
> image. If you mess around with the .vhd OS-9 size or change the offset
> value in RGBDOS, you can get cross contamination of the partitions.
> In short, the .vhd image is not a good determinator of where the 256 35-T
> drives start.
>
> Robert
>
>
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