4.2BSD boot from slave 1 disk

[Joseph S. D. Yao]

> I have a 4.2BSD  system I wish to boot from an ra81,  ...

>       ... Looking at /sys/mdec/raboot.s, it looks like
> either register R3 or R9 or both are involved in unit selection.
> However, I tried Depositing each with 1 during booting,
> and neither approach worked.  ...

The mdec raboot goes in the boot block.  It does not get read in
unless something else pulls it in.  In particular, on milo (a VAX
11/780), your floppy-disc program BOOT always gets read in first,
and then pulls whatever it wants off your hard disc.  On machines
like the 11/750, where you always ROM-boot off the first block,
you can change the unit number in R3 and get different units.  But
I don't believe that the 4.2 mdec/raboot will work for an 11/780.
In any case, you would have to go back to using the DEC VMB.EXE
loader with boot flags (R5) set to block boot (8).

Or, as Chris Torek points out, you can hack up /sys/stand/boot.c
to do the same thing.

	Joe Yao		hadron!jsdy at seismo.{ARPA,UUCP}