RT11 boot block 0 words ?

Jerome H. Fine jhfinedp3k at compsys.to
Wed Jan 4 19:31:48 CST 2006

 >Pete Turnbull wrote:

>>On Jan 4 2006, 21:49, Gooijen, Henk wrote:
>>I would like to use the vast knowledge of this community, as a brief
>>search through the calssiccmp archive gave no answer ...
>>I can't get RT11 booted anymore on my 11/34.
>>Is the first word (000240) the first word of block 0 of the RT11
>Yes, AFAIR all standard DEC bootstraps have 240 as the first word of
>the boot block.  240 is NOP.  Somebody once told me why they're done
>that way, but I can't remember; only that it seemed sensible at the
>time.  The only exceptions I know are the not-really-bootstraps on the
>first block of non-bootable RSX disks, which contain a little bit of
>code that prints something like "This is not a bootable disk" to the
>console, and then halts.
>It sounds a bit like your boot block has been wiped, and mostly
>replaced with zeros.  Can you load the first block off the disk
>manually, preferably not into location 000000, and examine it?  Should
>be fairly easy with an RL11.  Then try some other block and make sure
>that's not all zeros, to ensure it's the disk content you're seeing,
>not some problem with the controller.
Jerome Fine replies:

Tony is correct.  The boot block does start with
240 for the RL02.  If you know the approximate
version of RT-11 and the flavour of the monitor
(RT11FB, RT11XM, etc.), most of the rest of the
boot block at block zero can be described.  Of
course, if you did that, you also would have read
the RL02 pack!

One method of making sure that the RL02 pack is not
changed is to WRITE  PROTECT the pack so that it can't
be changed - PERIOD!  While some operating systems
can't run, RT-11 is PERFECTLY happy using this method
of making sure that the system disk (or any other for
that matter) is not altered.  Of course, you also can't
save any new files.  BUT, you can turn off the WRITE
PROTECT at any time and save one file at a time when
you actually have something to save.  NOTE that RT-11
must also write first to the directory, so if you use
this method, best to use VM: and copy the file in
one operation using PIP after the file is complete.

Sincerely yours,

Jerome Fine
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