[Info-vax] Tertiary VMB?

[Paul A. Jacobi]

It took me a while, but I finally remember how TERTIARY_VMB evolved!  It was 
almost 20 years ago...

TERTIARY_VMB.EXE is exactly the same code as VMB.EXE, except that 
TERITARY_VMB.EXE is linked with an image header.

MicroVAX systems have a version of VMB in ROM, and MOP load directly to 
NISCS_LAA.EXE.

Eventually LAN boot was needed on larger system, such as the VAX 8200. 
These systems do not have VMB in ROM.  LAN boot was implemented such that 
these systems first request TERTIARY_VMB.EXE, followed by a request for 
NISCS_LAA.EXE.

VMB.EXE does not contain an image header because the boot block must point 
directly to the code.  Without the image header, it became very difficult to 
identify the version of this file in patch kits.

However, MOP can served up images only with a valid image header.  VMB was 
simply relinked /HEADER/EXE=TERTIARY_VMB.EXE.

The Alpha WRITEBOOT code was enhanced to detect the image header. Instead of 
fixing up boot block to point first block of APB.EXE, it skipped over image 
header blocks to point directly to the code.  This eliminated the patch 
maintenance issue and the need for a tertiary image.


Paul A. Jacobi
HP OpenVMS Systems Group
Nashua, NH