[Simh] 8" Floppy disk image getting HALT error

[Clem Cole]

Paul - offered great info.   First are your sure these came from DEC
systems?  8" floppies were originally developed (by IBM to load microcode
on the 3330 disks) years before DEC started to use them.   IIRC DEC only
used them on PDP-8's and 11s.   The Vaxen and PDP-10 actually connected to
a PDP-11 front end that actually controlled them.

Second, as Paul said, trying to boot from them, unless you know what you
are doing is likely to cause a certain amount of madness, be a tad random.
   The trick would be to use the KryoFlux to get and image of the bits and
then start to work out from there what it is from the first we blocks.

Two more very important points ....

when dealing with floppies, you have to remember two important things....
format (hard or soft) and interleave.    Early [8" in particular] used hard
formatting.   I don't think DEC's version of the 8" ever did [ Paul is more
likely to remember that type of factoid].  With hard formatting you at
least know the number of sectors in each 'ring' - but you don't know how
the SW interleaved them.  Different systems interleaved in different ways.

The KryoFlux has to have some way to handle all of this but its going to be
important to know as much as we can about who the SW was configured when we
try too decode the first we blocks.   So you need to tell folks as much as
you can about how the data came off the disk when you grab it.

Good luck.

On Mon, Jul 10, 2017 at 4:16 PM, Paul Koning <paulkoning at comcast.net> wrote:

> PDP-11 disks are not necessarily bootable.  If they aren't, attempting to
> do so may just give you a halt, or spurious behavior.  Some systems
> initialize non-bootable disks with a dummy bootstrap that tells you "this
> is not a bootable disk", but you can't necessarily count on that.
>
> Apart from that, you attached an RK05 drive, so if you gave it your RX01
> image that can't work right because an RK05 is a very different device
> (4800 512-byte sectors).
>
> Several operating systems support RX01 and/or RX02.  The first few sectors
> of the disk will give a clue which OS you have (or more precisely, which
> file system layout, which is tied to the OS).  If you can post the disk
> image in some place where people can see it, you're likely to get some
> help.  If that's not an option but you can post the first 5 sectors or so
> as hex dumps, the file system type and thus the OS you'd need to interpret
> the contents is likely to become clear.
>
> paul
>
> On Jul 10, 2017, at 4:10 PM, Walker Sampson <Walker.Sampson at Colorado.EDU
> <Walker.Sampson at colorado.edu>> wrote:
>
> Hi everyone,
>
> Let me preface this by saying that I’m unfamiliar with the original PDP
> machines. I work as a digital archivist and have received 8” floppy disks
> from which I need to recover data.
>
> I believe I have recovered at least partial data from these disks; I’ve
> connected a Y-E Data 8” floppy drive to a KryoFlux floppy disk controller
> and gotten positive sector results setting the format to a DEC RX02 sector
> image. When I investigate the resulting disk image in a hex editor, I am
> seeing clearly a report document, so I don’t believe I have a false
> positive.
>
> Outside of observing in a hex editor however, I don’t know how to access
> the disk or its contents. Using SIMH, I haven’t gotten the virtual machine
> to boot the floppy disk image.
>
> Commands “AT RK01 <disk_image>” and then “BOOT RK01” give me a “HALT
> instruction, PC: 000002 (HALT)” message for the PDP-11 program. The PDP-8
> stalls indefinitely and the PDP-10 outputs “Non-existent device” as well.
>
> I can’t go back to the donors and ask what machines these 8” floppies were
> used with, so I’m not sure how to begin troubleshooting.
>
> Any advice in that area is much appreciated!
>
> Thanks,
>
> Walker
>
>
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