HP Vectra Technical Reference Manual page 329

10.5.1 Memory Allocation
The first step in the process is to allocate system memory for the EX-BIOS data area. This memory
allocation algorithm has two important features. First, by taking the memory size stored in CMOS
~
memory into consideration, it allows large driver data areas to be allocated in the EX-BIOS data
area. This method of expanding the EX-BIOS data area is explained in Section 9. Second, it
prevents invalid CMOS memory size data from preventing the system from booting. If the CMOS
memory size is set (using the SETUP utility or writing directly to the CMOS memory) such that
there is insufficient room for the EX-BIOS data area, this algorithm will adjust the value and write
the new value to CMOS memory. The EX-BIOS data area is required to support the EX-BIOS
extended features.
There are three important variables in this calculation.
• RAM_SIZE-This is the top of actual system memory. It is usually 256, 512, or 640 KB and
will always be an even multiple of 64 KB.
• EX-BIOS_SIZE-This variable is the size of the EX-BIOS data area, which is 4 KB in its default
config uration.
• CMOS_SIZE-This is the memory size stored in CMOS.
The CMOS_SIZE is checked for validity. If it is between 4 KB and 64 KB from RAM_SIZE, this
value is used as the base of the EX-BIOS data area. If CMOS_SIZE is more than 64 KB from
RAM_SIZE, the base of the EX-BIOS data area is located 64 KB below the top of actual system
memory. Finally, if CMOS_SIZE is less than 4 KB from the top of RAM_SIZE (or greater than the
top of actual memory), the base of the EX-BIOS data area is located 4 KB from the top of system
memory. The following formulas show this relationship:
If (RAM_SIZE-CMOS_SIZE)
>
4KB and
<
64KB
then EX-BIOS_SIZE
=
(RAM_SIZE-CMOS_SIZE).
If (RAM_SIZE-CMOS_SIZE)
>
64KB
then EX-BIOS_SIZE
=
64KB.
If (RAM_SIZE-CMOS_SIZE)
<
4KB
then EX-BIOS_SIZE
=
4KB.
The following examples illustrate this relationship:
In a 640 KB system, if CMOS_SIZE is 512 KB then the EX-BIOS_SIZE data area starts at 600
KB. This leaves an 88 KB free area between the EX-BIOS_SIZE data area and the memory
allocated to DOS.
320 System Processes