On 2017-07-11 21:09, Timothe Litt wrote:
VMS mount /over=id /foreign is the quickest way to identify files-11 and
RT disks. FILES-11 can be read directly; use EXCHANGE for RT-11. Once
you have the disk mounted on VMS, you can network it to wherever you like.
Similar story if you have RSX. I might have forgotten a thing or two
about VMS here, but I would have thought /OVER=ID/FOREIGN would not then
let you access the disk in the direct way if it is Files-11.
If you insist on doing things the hard way, there is low-level detail to
worry about.
The first track on DEC 8" floppies is reserved for boot (but not used)
in the standard RX01/2 formats. It's not used by any DEC OS. Not even
for booting (the DEC boot block is the first LBN following the reserved
track.)
Both are 77 tracks, 1 sided, 26 sectors/track. The rx01 is 128
bytes/sector; the rx02 256. So an RX01 image will be about 251KB, an
RX02 about 501KB.
Which then makes sense for data to start at track 26.
Logical blocks are 512 bytes; meaning that an LBN consists of 4 or 2
physical sectors. The physical sectors are interleaved. If you have a
physical dump of the disk (and your tools haven't outsmarted you), the
easiest thing to do is to de-interleave it.
Use the attached utility, which documents the format & will
interleave/deinterleave a floppy image using the usual interleave rules.
19D0(16) is close to 26 * 256 (short by 48 bytes), so I'd guess you have
an rx02 and are seeing the empty boot track. (Although not guaranteed,
the track was usually written with all zeroes).
I think Walked was a little careless in his conversion. He said bytes
0-6655, which actually turns out to be 01A0, or exactly where track 1
starts.
The 48 bytes may be left over from formatting, or an artifact of how
you're reading the medium. Or an indication that your recovery dropped
something. Hopefully it checks the CRCs..
Or just a conversion error. :-)
The E5 is probably left over from formatting. I think it was part of
the sync pattern, and that the formatter wrote
If you see 8-bit data, it's probably RT11 or Files-11. These are
self-identifying - block 1 (the second block) will have a filesystem
name in starting at byte 760(8). Will be DECFILE11A for ODS1 or
DECFILE11B for ODS2, DECRT11A for RT11. RSTS is also possible - I don't
remember it's code, probably DECRSTS11A. Given that, data
(deinterleaved), humans can easily tell what you have.
Unfortunately it's not that easy.
Files-11 do indeed have that identifier in block 1. RT-11 however, might
not. There is no requirement and no checking, and depending on what
version, and what tool, you might be lucky and find such a string there,
but the absence don't mean anything.
VMS Exchange helpfully enough actually writes "DECVMSEXCHNG" there.
(cut-and-pasted from a dump right here and now)
FLX (under RSX) do not write anything at all when you initialize the
disk with an RT-11 file structure.
I don't have any RSTS/E disk images to quickly peek into.
But with some detective work, you can still figure out if it is an RT-11
volume.
But the fact that the dump seem to get directly to document data without
anything at all suggest that there isn't any file structure at all on
the disk.
RT11 files are contiguous, so recovery is easy. FILES-11 files can be,
but probably aren't. You have to read mapping pointers. There are
tools that will do that (one of these daze I do intend to release mine.)
But it's much easier to just run EXCHANGE and say "COPY" by filename :-)
Indeed. Seems unneccesary work to write a tool to parse that out when
tools already exist. You can do it in VMS, or RSX, RSTS/E or Ultrix,
without having to write any code.
As for WPS-8 - yes, it's packed into 12 bits - but it's also encoded (I
vaguely remember it as a 6-bit code with shift & formatting - but I'd
have to look up the code I wrote to translate it.) In any case, it
would not look like text to a "modern" filesystem.
Yeah. I think we can exclude WPS from likely formats.
Johnny
Have fun.
On 11-Jul-17 13:26, 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"
<[email protected] on behalf of [email protected]> 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: [email protected] || 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: [email protected] || Reading murder books
pdp is alive! || tryin' to stay hip" - B. Idol
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