[sebhc] H8D files and labels

Dave Dunfield dave06a at dunfield.com
Wed Mar 29 05:39:49 CST 2006

> > Take ImageDisk for example - it is designed to replace TeleDisk (with
> > a documented format), and attempts to replicate EXACTLY the soft-
> > sector disk that was originally recorded - to this end, It records the
> > exact sector numbering and ordering, normal/deleted address marks,
> > maps for cylinder and head numbering to accomodate non-standard
> > formats, and quite a bit more - in short, I record everything I can
> > determine about the disk from the PC's FDC in the image file. I also
> > have a clear file identified with the IMD version and creation timestamp,
> > and an unlimited size comment field.
> > 
> > This is probably pretty close to what you describe...
> Now you're talking!  Could I get the doc for the Imagedisk format
> please?  I'd like to teach the SVD tools to use the format.  Off-list
> would make sense.

I just posted an updated to ImageDisk (1.12) to my site. The image
format is documented both in the documenation (TXT) file, and in the
on-line help. Go to:


Near the bottom of the main page, you will find a link called
"Disks/Software images". Select it, and ImageDisk is at the
very top of the selections offered for download.

> I'll remain in search of a "common image format" or a least a
> family of image formats (hopefully small number) that will stand
> the test of time, preserving these old disks and their
> ideosyncrasies upon which the hardware depended.

As noted in my previous post - I don't think you will find one general
purpose image format which suits everything. For two main reasons:

1) Physical medium differs
    The charactistics of the medium differ greatly, and you may find
    "new" formats which don't fit your previous general view.
     For example, NorthStar hard-sectored disks have essentially no
     header (sector data only). H17 disks have a small header, which
     include position and volume id. IBM format soft-sector has a different
     header with different information (and no volume ID). Apple disks are
     again completely different. And there are more (and weirder
     disks out there).

2) Intended purpose
    A "archival format" would try and replicate the content of the
    disk exactly - this would include details of interleave, and overhead
    bytes to describe details of the format down to the sector level, so
    that odd formatted disks can be preserved and recreated. If it is
    a "general" format, it would dedicate some overhead to describing
    the fields themselves. It would also have less concern that the image
    itself could be treated as a disk, so it might compress "all same"
    sectors etc. (which makes it tough to directly write new sector
    information into that sector).

   A "working format" image intented for use under a simulator might
   be more concerned about a layout which makes logical sense for
   seeking and reading tracks/sectors within the disk, and would make
   sure that the sectors are fixed-size so that they can be updated
   "on the fly". If the simulator for which it was created does not
   support oddly formatted disks, details required to record non-standard
   formatting may be ommitted - Like H8D, it might rely on the simulator
   to "know" some details about the disk format.

So, I think one needs to draw a line between archival storage and useful
storage. Ideally, we would define not so much a disk image format, but
an extemsible specification for storing the data for archive purposes,
which would be expanded as needed when new media types are added.
If everyone could agree on such a thing (unlikely), then the implementors
of the individual "useful" storage formats could provide tools to interpret
their images according that specification and possibly translate to and
from a "universal format" (If such a thing can be created).

In the meantime, I am happy if people just document their image
formats so I can access the content if needed.


dave06a (at)    Dave Dunfield
dunfield (dot)  Firmware development services & tools: www.dunfield.com
com             Collector of vintage computing equipment:

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