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"
<[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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