[sebhc] h17 and h8d disk images

Dwight K. Elvey dwight.elvey at amd.com
Wed Sep 1 16:12:14 CDT 2004

>From: "Dan Lanciani" <ddl-cctech at danlan.com>
>"Dwight K. Elvey" <dwight.elvey at amd.com> wrote:
>| I don't know if Dan is extracting the sector header information
>|and using that to determine the order of the sector blocks
>|or just reading the disk order.
>I'm using the headers.  Doing it any other way would make retries very
>difficult.  More specifically, I read an entire track (actually a track
>and a half), separate the data bits from the clock bits, and begin hunting
>for sectors which I scatter into a track image buffer.  For each sector that
>I validate I set a bit in a mask.  When I finish with the raw track I check
>the mask to see if I have found all 10 sectors.  If I have not I re-read the
>track and repeat.

Hi Dan
 This sounds good. It will keep us from getting things mixed up.
As long as you use the headers as part of your process, there should
be no issue.

>|It is true that all original
>|HDOS distribution disk have the natural order. This may not
>|always be the case. Dan mentions in a previous mail that the
>|only staggering he knew of was skewing but it was quite common
>|to use a 2:1 or 3:1 interleaving on HDOS disk ( you'll note that
>|my transfer program even has this option for creating disk ).
>Which H17 driver supported creating interleaved formats?

 I use many of the calls from the H17. I have lifted the format
code from the H17 code and patched in the interleaving. Once
the disk is formatted, the H17 doesn't care if it is interleaved
or not since it only looks at the headers to find sectors.
You can see my code in the H89LDR9.ZIP file, source
file H89LDR2.ASM. The idea of interleaving was done by many
others before me. I just added it to my code for those that
want it. As long as I'm reading and writing through H17
routines, it makes no difference other than time. HDOS it
self has an OS level interleaving like CP/M but it is not easily
modified at the OS level as CP/M is. There was an article in one
of the magazines, way back then, about doing the physical
interleaving for HDOS disk. I've long since lost that but remember
reading it. I know of a least one other user that had most of
their disks interleaved. I don't expect these to show up here since
it was a customer data base he used it with.

>| I guess the question for Dan is, do you assume that the physical
>|sector order matches the logical sector order when creating
>|your image files or do you map the logical sector order into
>|the order used in the images?
>I take the sectors as I find them but then (unless a special switch is

 It sounds like we are still in good shape. You'll just
have to watch out for any disk created with my transfer
code that someone chose to take advantage of the interleaving
option. It sounds like your code will bomb out on them.
Also, should you come on disk that fails in this way in
the future, don't assume that the disk is bad. It might
just be one of the few that are out there someplace that
have had this done to them by someone else.
 I do believe that you are OK in assuming that all release
disk were done without interleaving. There would be no reason
for them to do otherwise.

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