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<p class=MsoNormal>I added support for Dave Dunfield’s “ImageDisk”
disk image file format for soft-sectored floppies to the SIMH/AltairZ80
simulator. <o:p></o:p></p>
<p class=MsoNormal><o:p> </o:p></p>
<p class=MsoNormal>Dave Dunfield has many ImageDisk (IMD) disk image files on
his website at: <a href="http://www.classiccmp.org/dunfield/img/index.htm">http://www.classiccmp.org/dunfield/img/index.htm</a><o:p></o:p></p>
<p class=MsoNormal><o:p> </o:p></p>
<p class=MsoNormal>ImageDisk is an excellent format for storing disk images, because
the disk’s metadata is also retained by the format, allowing the image to
be written back to a floppy. I have used SIMH/AltairZ80 to create a disk
image for an S-100 system that I had, that I had no boot floppy for. I
added support for the disk controller to SIMH, then debugged the disk I/O
routines, tested it on the simulator, and wrote the image to a real 8”
floppy and it booted on the actual hardware on the first try. <o:p></o:p></p>
<p class=MsoNormal><o:p> </o:p></p>
<p class=MsoNormal>The ImageDisk support is implemented as a generic module
that has a simple sector read/write/format API. It supports all features
of the IMD file format, including non-standard sector numbering, and skewing.
The support is contained in two files, sim_imd.c, and sim_imd.h. In
addition to the ImageDisk library, I also wrote two disk controller cores, an
Intel 8272 (NEC765) and a Western Digital 179x. This has been tested
under Windows, Mac OS/X, and Linux, as well as big-endian Mac.<o:p></o:p></p>
<p class=MsoNormal><o:p> </o:p></p>
<p class=MsoNormal>Recently, I realized that DEC RX-01 floppies can be imaged
using ImageDisk since they are in the regular IBM single-density format.
I added support to the PDP-11 and PDP-8 RX02 disk simulation and was able to
boot RT-11 with it. I would like to contribute these enhancements to the
main SIMH distribution, and would welcome any feedback on the
implementation. The PDP-11 RX02 support has not been well tested.
While RX-02 floppies cannot be imaged by ImageDisk (due to the non-standard
formatting) being able to read and write RX-01 floppies is very useful for
transferring data to PDP-11’s and for possibly creating bootable media
using the simulator, which can then be used to revive actual hardware.<o:p></o:p></p>
<p class=MsoNormal><o:p> </o:p></p>
<p class=MsoNormal>The sim_imd support can be obtained by downloading the
source archive at: <a href="http://www.schorn.ch/cpm/intro.php">http://www.schorn.ch/cpm/intro.php</a><o:p></o:p></p>
<p class=MsoNormal>If anyone wants the PDP-8 and PDP-11 RX files, please let me
know and I will make them available.<o:p></o:p></p>
<p class=MsoNormal><o:p> </o:p></p>
<p class=MsoNormal>Using ImageDisk, I have recovered many 8” floppy disk
images, including 86-DOS, MP/M-86, Concurrent CP/M-86, OASIS, OASIS-86.
While I have a lot of these running in AltairZ80, I have imaged many more disks
(about 200) that I will get to doing something with as time permits. The
important thing is that the information can be preserved in a format that will
not degrade with time like the original floppy media. I have even found
that a very new Intel Core2 Duo Motherboard can still write single-density 8”
floppies, much to my surprise. Many PC motherboards cannot do this, but
given that a readily available $99 motherboard can do it, I think there is an
opportunity to save a lot more disks via imaging before the original media
decays further.<o:p></o:p></p>
<p class=MsoNormal><o:p> </o:p></p>
<p class=MsoNormal>-Howard<o:p></o:p></p>
<p class=MsoNormal><o:p> </o:p></p>
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