Re: Rescuing old 5.25" disks

[sirghoul@optonline.net]

On Tue, 17 Oct 2006 18:48:17 +0100, in comp.emulators.apple2 you wrote:

>[note crossposting]
>
>I think everyone agrees that as many old Apple II disks as possible should 
>be imaged as soon as possible, before they degrade to the point of 
>unreadability. And many people are imaging their disks and putting them on 
>archives like Asimov, which is good.
>
>But most of those images are in the dsk/do/po or nib formats. That's bad. 
>It's bad because those formats fail to preserve information about the disks 
>that is sometimes important, and it's *really* bad for two other reasons:
>
>   * Most of the tools that generate these formats don't do nearly enough 
>error checking, and the formats themselves have no checksum to guard against 
>corruption subsequent to imaging. There are probably dozens or hundreds of 
>subtly corrupt images on Asimov, and by the time anyone notices the 
>corruption it may be too late to reimage them. In many cases it's probably 
>already too late.
>
>   * Many disks can't be represented at all in either format. As far as I 
>know most games have been archived only in cracked versions, and while it 
>may be worth preserving those too, surely we shouldn't lose the originals 
>just for lack of an appropriate format.
>
I can't argue about the possibility of corruption, and I can't argue that there are bad images on Asimov, but I think
there may be one thing you've overlooked.

Many images on Asimov are of Cracked software, yes, and as such, the only thing the software on those images needs is
track/sector information. The cracked software has had the requirement for specialized information removed from it,
making it useable in a standard DOS/Prodos/CPM environment.

These particular environments almost always only care that the Track Sector information is properly ordered, and that
order is built into the standards for .do and .po images.

.dsk images are, effectively, an 'I don't know WHAT order things are in here, so the emulator will have to figure it
out.' and I have not yet come across a .dsk that has not worked UNLESS it was corrupted.

There are a very few pieces of software out there that won't work in any of these formats, because they do indeed fail
to preserve the information that these uncommon programs need. Usually, this is the Disk Volume Number, which is not
preserved in any of the above mentioned images

This is the purpose of the .nib format, which is nothing more than a nibble-by-nibble exact copy of the original disk,
protection and all. anything non-standard on the disk, short of track-arcing, 1/4 tracks, and other such esoteric
protection schemes is preserved in the image, <grin> giving you a copy-protected copy of your copy-protected disk.

That you can copy.

For the more esoteric protection schemes, cracked versions are already out there, and are for nearly everyone, the norm.

I'm not saying don't bother with coming up with more exacting ciopying schemes. Not am I saying don't develope the tools
necessary to implement them. I'm saying that the existing standards - from what I've seen - seem to work for 99.999% of
what's out there.

John.


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