System Initialization and Acceptance Testing (Normal Operation)
4.7 Operating System Bootstrap
Figure 4–3 Memory Layout Prior to VMB Entry
PFN bitmap
(always on page boundary and
size in pages n = (# of MB )/2)
Firmware "scratch memory"
(always 16 KB)
Q22-Bus Scatter/Gather Map
(always on 32 KB boundary)
Potential "bad" memory
.
.
.
.
.
.
.
.
PFN bitmap
QMR base
Top of Memory
n pages
32 pages
64 pages
0
Balance of 128 KB block
to be used for SCB, stack,
and the secondary bootstrap.
VMB image
Reserved for RPB, initial stack
Potential "bad" memory
.
.
Base
Base+512(SP,PC)
256 pages for VMB
128 KB block of
"good" memory
(page aligned)
MLO-008455
Unused memory
4.7.2 Primary Bootstrap Procedures (VMB)
Virtual Memory Boot (VMB) is the primary bootstrap for booting VAX
processors. On the KA681/KA691/KA692/KA694 module, VMB is resident
in the firmware and is copied into main memory before control is transferred to
it. VMB then loads the secondary bootstrap image and transfers control to it.
In certain cases, such as VAXELN, VMB actually loads the operating system
directly. However, for the purpose of this discussion "secondary bootstrap"
refers to any VMB loadable image.
4–26 System Initialization and Acceptance Testing (Normal Operation)
