[sebhc] Disk formats and emulators

Steven Parker sp11 at hotmail.com
Mon May 10 19:43:06 CDT 2004

Eric says:
>...the Dave W format was moving that way...though
>was never (as far as I know) completed.

It's definitely not in the version you can download from his website.

>I think we should consider standardizing on this format, again, even though 
>it isn't ideal.

It may be worth considering other options, particularly at this time.  A few 
issues that come to mind are  (1) It was intended to load a hardware device 
(like hex dumps are used to load prom burners). (2) the text file requires 
conversion both before and after it's used (assuming the implementation 
makes the disk writable).  (3) If you don't have a hardware SVD or dont' 
want to hold the entire image in memory while working with it, the text 
format would significantly complicate paging.  (4) More direct formats would 
require about the same space as the capacity of the disk being stored.  The 
SVD format requires 3-4 times as much space, and even more with track 
comments. (5) While the text format is "readable", I'm not sure it's 
particularly useful to do so.  And creating readable dumps of binary files 
is trivial on most platforms. (6) It's not analagous to the more direct 
format already being used to store and emulate tape files (.PID, .tape). (7) 
There's no facility in the format to verify data integrity (as there is in a 
real disk).  I was able to identify damage to one of the HUG files in the 
archive and reconstruct it because it was missing a byte entirely - a 
changed but still present byte would have been impossible to detect.

I like the header in the SVD format, but I'm still not sure if it's really 
needed.  It's possible that information can be uniquely implied just by the 
size of a binary file.

My preference of the moment would be to store disk images in a binary 
format, which would have integral crc's and might include some additional 
information, to take advantage of the storage savings and more direct 
usability in new emulators.  A tool could be provided in the archives to 
convert to the SVD format for those using actual SVD's or old emulators.

The additional information could potentially be provided by an associated 
description file which would include label information.

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