[Simh] 8" Floppy disk image getting HALT error

[Walker Sampson]

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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