On Sunday, March 24, 2013 at 2:20 PM, Anders Magnusson wrote:
This issue came to light due to efforts to use NetBSD with the
latest simh's new VAX simulators (VAX 11/730, VAX 11/750 and VAX
8600/8650). All of these systems use VMB to initiate the bootstrap
process and since the disk being booted doesn't contain a Digitial
ODS2 disk structure, they boot using they achieve a boot using the
bootstrap code provide in sector 0 of the device being booted. The
systems with ROM based VMB have built in code in the ROM VMB to use
the pointers describing the bootstrap location in sector 0 to
directly load the rest of the bootstrap (usually from sectors 1 thru
13) and dispatch to that.
You are not supposed to use VMB on those big machines. You should
load boot directly from the console media.
This is how all BSDs always have worked.
I guess that might be possible (even on a VAX 11/750, you could always
boot thru the console TU58). Given hard booting a dedicated loader program
the details of the boot block won't matter. However, you'd still have to make
the TU58 media bootable. The 750 Boot procedure (for any device) loads
sector 0 and starts execution at offset 2 of the 512 bytes loaded. There
current isn't any code in sector 0.
This seems to be the installboot bug, yes. But in some way it must get the
boot code installed sometimes; I installed NetBSD 6 on a fresh
4000/600 just a few months ago. It had VMS on its disks before. (Or maybe I
did some creative to get it work but do not remember it :-)
You didn't have to do anything special. The 4000/600 has a ROM base VMB
version which doesn't need any code in sector 0.