[Simh] 8" Floppy disk image getting HALT error

[Johnny Billquist]

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