From: jnc@mercury.lcs.mit.edu (Noel Chiappa)
Subject: [TUHS] Determining what was on a tape back in the day
Date: Sun, 19 Nov 2017 08:41:09 -0500 (EST) [thread overview]
Message-ID: <20171119134109.59F3018C0F5@mercury.lcs.mit.edu> (raw)
> From: Will Senn
> I don't quite no how to investigate this other than to pore through the
> pdp11/40 instruction manual.
One of these:
https://www.ebay.com/itm/Digital-pdp-Programming-Card-8-Pages/142565890514
is useful; it has a list of all the opcodes in numerical order; something none
of the CPU manuals have, to my recollection. Usually there are a flock of
these "pdp11 Programming Cards" on eBait, but I only see this one at the
moment.
If you do any amount of work with PDP-11 binary, you'll soon find yourself
recognizing the common instructions. E.g. MOV is 01msmr (octal), where 'm' is
a mode specifier, and s and r are source and destination register
numbers. (That's why PDP-11 people are big on octal; the instructions are easy
to read in octal.) More here:
http://gunkies.org/wiki/PDP-11_architecture#Operands
So 0127xx is a move of an immediate operand.
>> You don't need to mount it on DECTape drive - it's just blocks. Mount
>> it as an RK05 image, or a magtape, or whatever.
> I thought disk (RK05) and tape (magtape) blocks were different...
Well, you need to differentiate between DECtape and magtape - very different
beasts.
DECtape on a PDP-11 _only_ supports 256 word (i.e. 512 byte) blocks, the same
as most disks. (Floppies are an exception when it comes to disks - sort
of. The hardware supports 128/256 byte sectors, but the usual driver - not in
V6 or V7 - invisibly makes them look like 512-byte blocks.)
Magtapes are complicated, and I don't remember all the details of how Unix
handles them, but the _hardware_ is prepared to write very long 'blocks', and
there are also separate 'file marks' which the hardware can write, and notice.
But a magtape written in 512-byte blocks, with no file marks, can be treated
like a disk; that's what the V6 distribution tapes look like:
http://gunkies.org/wiki/Installing_UNIX_Sixth_Edition#Installation_tape_contents
and IIRC 'tp' format magtape tapes are written the same way, hardware-wise (so
they look just like DECtapes).
Noel
next reply other threads:[~2017-11-19 13:41 UTC|newest]
Thread overview: 47+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-11-19 13:41 Noel Chiappa [this message]
2017-11-19 14:55 ` Clem cole
2017-11-19 21:00 ` William Corcoran
2017-11-19 21:19 ` Ron Natalie
2017-11-19 22:00 ` Dave Horsfall
2017-11-19 22:38 ` Lyndon Nerenberg
2017-11-19 22:40 ` Ronald Natalie
2017-11-19 23:41 ` Dave Horsfall
2017-11-20 1:02 ` Ronald Natalie
2017-11-20 1:18 ` Dave Horsfall
2017-11-20 18:12 ` Random832
2017-11-20 23:22 ` Dave Horsfall
2017-11-20 23:35 ` William Pechter
2017-11-21 0:01 ` Ron Natalie
2017-11-20 19:02 ` Paul Winalski
2017-11-19 14:55 ` Will Senn
-- strict thread matches above, loose matches on Subject: below --
2017-11-20 19:42 Noel Chiappa
2017-11-20 17:00 Noel Chiappa
2017-11-20 16:01 Noel Chiappa
2017-11-20 17:37 ` Will Senn
2017-11-19 20:46 Steve Simon
2017-11-19 18:45 Noel Chiappa
2017-11-19 17:49 Noel Chiappa
2017-11-19 18:35 ` Arthur Krewat
2017-11-18 19:23 Noel Chiappa
2017-11-18 21:32 ` Will Senn
2017-11-18 21:49 ` Warren Toomey
2017-11-18 18:34 Noel Chiappa
2017-11-18 18:37 ` Ronald Natalie
2017-11-18 18:40 ` Ronald Natalie
2017-11-18 21:51 ` Dave Horsfall
2017-11-18 21:07 ` Will Senn
2017-11-18 22:53 ` Clem Cole
2017-11-19 1:47 ` Will Senn
2017-11-18 16:39 Will Senn
2017-11-18 18:57 ` Clem Cole
2017-11-18 20:03 ` Don Hopkins
2017-11-18 22:37 ` Dave Horsfall
2017-11-18 23:16 ` Don Hopkins
2017-11-18 23:35 ` Arthur Krewat
2017-11-19 0:35 ` Steve Nickolas
2017-11-19 0:42 ` Don Hopkins
2017-11-19 1:04 ` Clem cole
2017-11-19 16:20 ` Arthur Krewat
2017-11-20 2:33 ` Lawrence Stewart
2017-11-18 21:26 ` Will Senn
2017-11-18 22:39 ` Clem Cole
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=20171119134109.59F3018C0F5@mercury.lcs.mit.edu \
--to=jnc@mercury.lcs.mit.edu \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).