[Coco] CoCoSDC question: default .DSK size?

[Allen Huffman]

> On Dec 17, 2014, at 6:44 PM, Darren A <mechacoco at gmail.com> wrote:
> 
> On Wed, Dec 17, 2014 at 5:01 PM, Allen Huffman <alsplace at pobox.com> wrote:
>> Does this mean if I do:
>> 
>> DRIVE 1,"42TRACKS.DSK",NEW
>> 
>> ...then I write to track 42, it *will* become a 42 track disk image?
> 
> 
> It will for as long as it remains mounted.
> 
> Since the image has no header, the *next* time it is mounted the rules of
> the disk geometry table will be applied. Having more than 40 tracks, it
> will be treated as a double-sided image.

Ah, that is very good to know. Therefore, it can’t really tell the difference between a 40 track double sided disk image, and an 80 track single sided, without the header. It has to assume, but then it still works the same (sector 0 - sector n) I guess.

> You could choose to initially create your DSK images as 42 track
> double-sided images before copying anything onto them. It's a little
> wasteful of space, but you eliminate the need to manually insert a header.
> 
> The program below can be used to create a 42 track double-sided DSK image,
> mounting it in drive 1.
> 
> 10 CLEAR 200:F$=STRING$(128,255)
> 20 INPUT "NEW DSK FILE";D$
> 30 DRIVE 1,D$,NEW
> 40 DRIVE 1,2
> 50 DSKO$ 1,13,18,F$,F$
> 60 DRIVE 1,UNLOAD
> 70 DRIVE 1,D$
> 80 FOR S=1 TO 18
> 90 DSKO$ 1,17,S,F$,F$
> 100 NEXT

Man, too many years. DSKO$ is drive, track and sector, then two 128 byte strings (because a string couldn’t be 256 bytes?). Is that right?  Track 13 was the directory track?

In the case of the common Disk BASIC patches, double sided was used, but each side was treated like a single 40 track disk since having more than that needed more memory for the allocation table and stuff and broke compatibility. However, it seems likely I will have some disks like that too — but I would copy them as separate floppies (DIR 0 was one side, DIR 1 was the other) since that’s really what they were.

For OS-9, though, a double sided image would be needed.

I am starting to dread all the various disk formats I am going to run in to, going back to 1983 ;-) Yipes!

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