[Simh] 8" Floppy disk image getting HALT error

Tue Jul 11 17:44:37 EDT 2017

Timothe Litt brought up that track 0 is probably not actually used.
I was just trying to remember that one myself, so there is probably 
your explanation for all the zeroes in the beginning.

Size looks good. An RX01 should be about 128Kbyte, while an RX02 should 
be about 256Kbyte.

To mount it, you should obviously say that it is an RX02. If you try 
RX01, it will also be wrong for various reasons.

Data starting at byte 6657 indicates that it start right up at sector 
26. If there is nothing before, and nothing after the document, that 
makes it sound as if the data was written direct to the disk without any 
file system at all. Definitely nothing bootable in there, or else you'd 
find lots of binary junk before that text.

The zeroes and e5e5e5e5 values seems to just be filler in there.

   Johnny

On 2017-07-11 19:26, Walker Sampson wrote:
> Hi everyone,
>
> Many thanks for this feedback. A fair amount to chew on here. I’ve sent a request to the donor to share the disk image, if I get a positive I’ll be happy to throw up a Dropbox link to it for others to examine.
>
> This may mean a problematic read of the disk itself, but addresses 00000 – 019D0 are all zeroed out, or about bytes 0 – 6655.
>
> Data begins at byte 6657, and that is the document I mentioned. Last byte of the document is 73080 and then just blocks of either zero or E5E5E5E5 till the end of the disk.
>
> To Paul’s point of mounting a RK05 drive – which drive should I be mounting here, assuming it is the RX02 disk it seems to be? “AT RX01 <disk_image>” still gets a HALT error. Of course, as you all point out, perhaps this isn’t a bootable disk, period. “SH RX01” gives “RX1, 256KB, attached to test-decrx01.img, write enabled”
>
> FYI as well, on a modern HFS+ system, the disk image file is coming in at 256 KB.
>
> Any thoughts on the run of zeroes and E5E5E5E5?
>
> Thanks again,
>
> Walker
>
>  On 7/11/17, 6:29 AM, "Simh on behalf of Johnny Billquist" <simh-bounces at trailing-edge.com on behalf of bqt at softjar.se> wrote:
>
>     Hi.
>
>     On 2017-07-10 22:10, Walker Sampson 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
>
>     To sum things up. You can probably ignore all the questions about if
>     this really is some DEC floppy, what kind of format it has, and so on.
>     If kryoflux managed to extract data that looks valid with RX02 parameter
>     settings, then I'd say we can be sure it is an RX02 disk. And this
>     format was unique to DEC, so it can't be anything else.
>
>     Which also means, you already have managed to exact all the bits, and
>     most probably correct. The next question is just about restoring the
>     data in a more coherent form, which means getting it in the form of
>     files, and understanding the format of the files.
>
>     For this, we need to know what system the floppy was written on. Paul
>     Koning gave the most useful advice. The first few blocks will usually be
>     enough to find out what system the floppy was written on.
>
>     RX02 floppies could certainly be bootable, but most are not. OS/8 (and
>     derivatives) for the PDP-8, and RT-11 for the PDP-11 were the ones that
>     supported RX02 as a bootable system. Other systems supported the
>     floppes, but only as a way of carrying bits around, so not being able to
>     boot from the floppy is probably to be expected.
>
>     So, if you could give us just the first few blocks, it should be
>     possible to tell what file system it has, and that gives us OS, file
>     structure and probably the ability to work out the rest in quick order.
>
>     	Johnny
>
>     --
>     Johnny Billquist                  || "I'm on a bus
>                                        ||  on a psychedelic trip
>     email: bqt at softjar.se             ||  Reading murder books
>     pdp is alive!                     ||  tryin' to stay hip" - B. Idol
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-- 
Johnny Billquist                  || "I'm on a bus
                                   ||  on a psychedelic trip
email: bqt at softjar.se             ||  Reading murder books
pdp is alive!                     ||  tryin' to stay hip" - B. Idol