ImageDisk/Site update posted.

Dave Dunfield dave04a at
Thu Aug 4 11:01:10 CDT 2005

At 10:38 AM 8/4/05 -0500, you wrote:
>Dave Dunfield wrote:
>> Hi Guys,
>> I have posted the update to ImageDisk which allows it to work
>> with Head/Cylinder values on a per-sector basis if needed.
>> I have also posted a number of additional ImageDisk format
>> system disk archives.
>Dave, from my quick read of your description of the IMD format, there is meta 
>information that I think would be valuable to store.  When a disk is imaged, the 
>captured file should indicate which tracks/sectors had problems being read. 
>That would allow automated merging of two different attempts to capture a given 
>disk (I haven't used your merge program, but my understanding was that one had 
>to manually specify which tracks to take from each image.  Futher, when 
>archiving one often is processing a large batch of disks.  Keeping track of the 
>problematic sectors manually and making sure that information is associated with 
>the disk is challenging.  Some months later when going back to a pile of disk 
>images, it would be nice to know which sectors are suspect.


I *DO* keep track of which sectors could not be read. If you look at the SECTOR
DATA RECORD, you will see that it consists basically of a flag byte followed by
the sector data. The flag bytes are:

 00 = Sector unavailable (no data follows)
      This means that the sector could not be read from the original master.

 01 = Normal sector data (sector-size data bytes follow)
      Self explainatory.

 02 = Compressed sector data (1 byte follows)
      This means that the entire sector was read and found to have all bytes
      containing the same data value - IMD will automatically expand this sector-size
      occuranges of the data value - it's primary purpose is to reduce the storage
      required by unused areas of the disk.

My analyze/merge utility will automatically extract 01 or 02 sectors from one image to
fill in 00 "holes" in another. It will also warn you if 01 or 02 sectors occuring on
both disks don't logically match (in which case you probably shouldn't be merging them).

At this time I DO NOT keep track of the occurance of soft/recoverable read errors. In
my experience these have more to do with the particular PC/FDC/DRIVE combinarion and/or
individual disk condition, and I do not believe the added complexity/size of collecting
and recording such details will be worth it...

ImageDisk will display sector read errors, and unavailable sectors as it records the
disk, and analyze/merge will display a summary of the Unavilable, NormalData and Compressed
sectors occuring within an image, as well as a detailed track by track summary if requested.
For me this gives me pretty much everything I can actually make use of.

dave04a (at)    Dave Dunfield
dunfield (dot)  Firmware development services & tools:
com             Vintage computing equipment collector.

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