27 May
2025
27 May
'25
5:17 p.m.
Yufeng Gao wrote:
The s1 tape is a UNIX INIT DECtape containing the
kernel, while s2 includes
most of the distribution files.
[https://www.tuhs.org/pipermail/tuhs/2025-February/031420.html]
Hello Yufeng,
Do you have more details on the format of the s1 tape? I want to reproduce your
work.
The s2 tape is in the tap format, which was easy to decode, and I assumed that
s1 was similar, just with its file headers on an earlier tape. I’ve been able to
fairly accurately segment s1 into files by observing that blocks duplicate the
tail of the previous block when they are not a full 512 bytes. I’ve written a
tool for this and have segmented all the text files and some of the binaries,
but I’m floundering on the rest. What you say seems to suggest that s1 actually
does have file metadata.
Thalia
27 May
27 May
9:22 p.m.
New subject: 1972 UNIX V2 "Beta" Resurrected
https://en.wikipedia.org/wiki/DECtape
It's more like a very slow floppy drive than like a tape. You may have
DECtape-I (tu56) or DECtape-II (tu58). If it's DECTape-II,
https://retrocmp.com/tools/tu58fs is probably what you want; it doesn't do
great for VAX 11/730 booting, but it should be OK for file extraction.
SIMH has reasonable support for both -I and -II devices but you may have to
pull the code out and make your own tool--I don't know of a tu58fs
equivalent for tu56.
Adam
On Tue, May 27, 2025 at 10:18 AM Thalia Archibald via TUHS <tuhs(a)tuhs.org>
wrote:
Yufeng Gao wrote:
The s1 tape is a UNIX INIT DECtape containing the
kernel, while s2
includes
most of the distribution files.
[https://www.tuhs.org/pipermail/tuhs/2025-February/031420.html]
Hello Yufeng,
Do you have more details on the format of the s1 tape? I want to reproduce
your
work.
The s2 tape is in the tap format, which was easy to decode, and I assumed
that
s1 was similar, just with its file headers on an earlier tape. I’ve been
able to
fairly accurately segment s1 into files by observing that blocks duplicate
the
tail of the previous block when they are not a full 512 bytes. I’ve
written a
tool for this and have segmented all the text files and some of the
binaries,
but I’m floundering on the rest. What you say seems to suggest that s1
actually
does have file metadata.
Thalia
31 May
31 May
10:41 a.m.
New subject: 1972 UNIX V2 "Beta" Resurrected
Do you have more details on the format of the s1 tape?
I want to reproduce your
work.
Hi Thalia, I documented the format in the readme for the Dennis Tapes
(https://www.tuhs.org/Archive/Applications/Dennis_Tapes/README)
The 's1' tape is a 'UNIX INIT DECtape' used for cold booting UNIX,
from a
version of UNIX between V1 and V2. It was created by the rather poorly
documented maki command, and therefore not readable by most tools. The format
consists of a boot block, a dump of the last 32 KiB of the RF disk /dev/rf0
and a small set of important programs. The boot block is the vcboot program
described in bproc(7). The 32-KiB dump consists of the bos, Warm UNIX, Cold
UNIX and an unassigned program, with the bos occupying 2 KiB, Warm and Cold
UNIX occupying 12 KiB each and the unassigned program occupying 3 KiB. The
remaining 3 KiB is slack space from the RF disk. The files on the tape are
stored in a way similar to tar(1), albeit in a more primitive way. All files
are stored consecutively with a directory block followed by file data. A
directory block consists of a 16-bit file size field, an 8-bit mode field, an
8-bit user ID field and a null-terminated path field. End of directory is
marked by setting the file size field to 0. Given the limitation of this
format and the fact that group IDs did not exist back then, timestamps and
group IDs are all set to 0 in the converted tar(1) archive.
Here is a block map of the tape I made last year:
578 blocks, 98 (16.96%) used, 480 (83.04%) free.
B = boot; D = directroy;
. = free; X = file data;
O = bos; W = wunix;
C = cunix; S = rf slack;
U = unassigned program;
|0123456789ABCDEF
--+----------------
00|BOOOOWWWWWWWWWWW
01|WWWWWWWWWWWWWCCC
02|CCCCCCCCCCCCCCCC
03|CCCCCUUUUUUSSSSS
04|SDXDXDXDXXDXXXDX
05|DXXDXXXXXXXXDXXX
06|XD..............
07|................
The actual decoding of the filesystem is done by the Cold UNIX kernel, the boot code
simply restores the bootloader and kernel to the last few tracks of the RF, if I recall
correctly.
I’ve written a tool for this and have segmented all
the text files and
some of the binaries, but I’m floundering on the rest. What you say
seems to suggest that s1 actually does have file metadata.
The text files are actually leftovers from a previous backup of UNIX V3-ish source code,
which used the tap(1) format. The header got overwritten by the s1 UNIX INIT DECtape, so
there's no metadata left.
Sincerely,
Yufeng
13
days inactive
17
days old
2 comments
3 participants
participants (3)
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Adam Thornton -
Thalia Archibald -
Yufeng Gao