Bootstrap Idea

Bob rjm at
Fri Sep 12 19:07:35 AEST 1997

>	I had an idea about bootstrapping images into PDP-11s, please shoot
>it down! Ok, I don't know much about the -11 hardware, how hard would it
>be to bootstrap as follows:
>	hand-toggle in a small bit of code, which
>	sucks in a bigger bootstrap over a serial line, which
>	then can pull in a disk image over the serial line & write to disk

Well, for what it's worth here's my contribution. I have been able to
set up working v5 and v6 systems on my 11/34c (which uses an RK05
drive) uisng the distributed images (thanks Warren). 

The key here I think is to make use of the excellent work that has
been already done on the various PDP-11 emulators. The emulator I use
is that of Bob Supnic, which runs wonderfully on my Linux box.

v6 is available as an image of a tape. The docs helpfully say:

This is a copy of the Sixth Edition distribution tape which was sent
to me by Ken Wellsch. The file v6.tape.gz is the tape image, with the
first 100 512-byte tape blocks containing tape bootstrap stuff. Blocks
100 - 4099 are the RK05 root image, blocks 4100 - 8099 are the /usr
RK05 image, and the blocks 8100 - 12099 are the /doc RK05 image.

It is trivial with the UNIX command dd to split the tape image into
its constituent parts:

	1) Tape bootstap (useless for me)
	2) RK05 root image
	3) RK05 /usr image
	4) RK05 /doc image

I can then start the Supnic emulator, attach the three RK05 images to
drives 0, 1 and 2 and boot. My system has only a single RK05 drive. As
a result I had to mess around in the emulator to create a fresh RK05
image containing a useful subset of the root and /usr images. In
practice it's not too hard to get v6 onto a single RK05 pack -- I
think it's only necessary to lose stuff like the spell disctionary and
so on.

I also wanted support for a second DL11 serial line, so I used the
emulator (and some extra emulated disk space) to rebuild the kernel.

Once I was happy with the disk image I'd created, it was time to
transfer it to real hardware. My 11/34c runs RT11 and I was able to
get hold of a small stripped down Kermit server-only program from John
Wilson. I forget the name of this utility, but it's available from The stardard RT11 Kermit that I have is unable to
transfer entire disk images, the Wilson implementation can do so.

Booting the 11/34c from RX01 floppy (one RK05 drive only, remember) I
ran the Kermit server. From the PC end it was straightforward to
transfer the image: "PUT imagefile.img RK01:". Aside from a
spectacular RK05 head crash that put my machine out of action for a
while, all was well.

For v7, I started with a single RL02 image. That would boot on the
simulator. I added a couple of emulated RK05s to the emulator set up
and proceded to build a single RK05 which would (just!) hold a
bootable v7 image. I warn you that v7 on a 2.5Mb disk is tight, but it
can be done. Having built the image, I rebuilt the kernel to enable
RK05 support (and a second serial line, again) and disable the other
disk drivers. That kernel went onto my new image. Again, the same
Kermit trick enabled the image to be transferred to the 11/34a.

If anyone wants these RK05 bootable image files, please let me know
(rjm at - not this address)!

A few points though:

1) RK05s packs _can not have_ bad blocks. There is no bad block
revectoring on these drives. A bad block on a pack suggests the pack
is ready for the dumpster. This makes life a little easier. I'm not
sure how you'd deal with bad block revectoring on an RL01/RL02 for
example. I guess it's not too hard, but I shan't speculate there.

2) My 11/73, on the other hand, uses an RD53 (last time I looked). I'm
not sure if the emulator can deal with these kind of drives. In any
case, support for MSCP drives only came with 2BSD, which I've not
played with. Maybe the same emulator tricks can be employed to get
RDxx images, modulo the bad blocks problem.

3) If you don't have a PDP-11 operating system running, the Kermit
approach won't be much use. There may be a stand-alone file transfer
program that can write to raw devices. No idea -- perhaps someone
needs to write this (both for the PDP and the PC ends).

Hope this helps.


Bob Manners                       (My REAL address is: rjm at

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