HP Vectra Technical Reference Manual page 376

B.3.1 Option ROM Data Segments
An option ROM which does not have available on board RAM can get memory in the manner
described above. However, the problem arises as to how the option ROM is to 'remember' the
data segment if it doesn't have any RAM to save the segment in. This problem usually can be
solved since most option ROMs are accessed through the software interrupt mechanism. The
option ROM adapter simply directs its entry point software interrupt vector to its EX-BIOS RAM
data segment which in turn jumps to the option ROM's entry point. That is,
80286 INT nn
-+
EX-BIOS data segment
-+
option ROM
PUSH CS
POP OS
JMP FAR ROM_ENTRY_POINT
,. Load option ROM OS
B.3.2 EX-BIOS Global Data Area
The EX-BIOS global data area is shared between several EX-BIOS drivers. It contains temporary
and permanent variables required by the EX-BIOS to function properly. Some of these variables
can be modified by application programs. As with the STD-BIOS data area, care should be taken
when modifying the EX-BIOS data area.
The EX-BIOS global data area can be found by calling the V_SYSTEM driver, with the function
F_INS_BASEHPVT. The EX-BIOS global data area segment will be returned in the DS register.
Table B.12 defines the contents of this area.
Memory Map 367