[Coco] Emulator Disk sizes - was Crunch? Urbane

[Robert Gault]

Paul Fitch wrote:
> I've tried other emulators and I like VCC the best.  That does not mean that
> I consider it to be "finished".  I will say that I've been a bit of a file
> hound in the last 18 months or so, and this is the FIRST disk I've ever
> tried to use that was rejected.  I noticed right away that it was smaller
> than the hundreds of other .DSK and .OS9 disk images I have in my
> possession.
>  

The problem is not unique to VCC, although this particular aspect is. 
Even with disks of the full 35 track size, VCC will look at LSN0 and 
frequently fail if that sector has data.

There was/is a problem with the way NitrOS-9 disks are distributed. All 
these disks are labeled .dsk but don't completely adhere to the JVC 
format. They frequently were shorter than they should be and never had 
the extra optional header that indicates the number of sides and size. 
As a result, they only work with MESS when the extension is changed from 
.dsk to .os9 . Once done, MESS knows that it must read LSN0 to determine 
the size and structure of the disk image.

There are also problems with support programs that create disk images, 
as many do not create valid Disk Basic directories. The second 16 bytes 
of each directory entry should be all $00 if unused. If that is not 
true, Tandy's Disk EDTASM+ will fail as it uses those 16 bytes to 
determine file sizes.