[Info-vax] Backup TK50 tapes

[Johnny Billquist]

On 2013-02-27 14:28, Paul Sture wrote:
> In article <kgjof8$e0l$1 at Iltempo.Update.UU.SE>,
>   Johnny Billquist <bqt at softjar.se> wrote:
>
>> On 2013-02-26 23:15, Bob Koehler wrote:
>>> In article <kgj03k$2ke$1 at Iltempo.Update.UU.SE>, Johnny Billquist
>>> <bqt at softjar.se> writes:
>>>>
>>>> Anyway, the problem with bootable tapes, at least on a PDP-11, is that
>>>> your tape starts with a boot block. That block is read into memory, and
>>>> the boot rom jumps into the code read in. This boot block on the tape is
>>>> outside of what is visible as files on an ANSI-labelled tape. So you
>>>> cannot see, or access this block except by doing low level reads from
>>>> the tape. Any tool like COPY is unable to see or access this data.
>>>
>>>      Interesting.  On VAXen, bootable tapes tended to keep all thier files
>>>      in ANSI labeled files.  Thus the earlier post the the TK started with
>>>      VMB.EXE.
>>
>> But then the boot roms needs to understand the ANSI tape format, read
>> through tape headers, parse stuff, locate the right file, read it into
>> memory, and then execute it. Even to the point of possibly understanding
>> the format of the executable.
>> That's a heck of a lot to have in the rom image. And what if you want to
>> boot something that use a different tape format? Unix bootable tape
>> distributions have never been ANSI labelled tapes, for instance.
>
> And IIRC 11/780 boot floppies were written in RT-11 format, which was a
> lot simpler.

Correct, I think.
I know that the RL02 on the 86x0 machines holds a full RT-11 system, as 
that is what the FE is running there.
Very simple file system, and the VAX was booted by that thing.

When you initially installed VMS, you booted the standalone backup 
system from the FE device. RX01 for the 11/780, TU58 for the 11/750 and 
RL02 for the 8600. And that system of course could access tapes and 
restore savesets to disk, and so on...

If you were to boot some kind of Unix from scratch, it became much more 
"interesting".

	Johnny