Hi,

I am wondering if my option ROM can use Extended BIOS Data Area (EBDA)
to store some (very) small data (around 16bytes)? Which area in EBDA
is safe and guaranteed for my option ROM?

Do anybody know any updated documentation about EBDA?

Thanks,
J

On Apr 3, 12:34�am, junkoi  <spamt...@crayne.org> wrote:
> Hi,
>
> I am wondering if my option ROM can use Extended BIOS Data Area (EBDA)
> to store some (very) small data (around 16bytes)? Which area in EBDA
> is safe and guaranteed for my option ROM?
>
> Do anybody know any updated documentation about EBDA?
>
> Thanks,
> J

I don't know of any 'up to date' documentation.  The EBDA originated
with the IBM PS/2 line, in their bios, from what I've gathered, and
like many things IBM started, it got incorporated into other bios's,
like Phoenix's, if you have a PS/2 type mouse then your system likely
supports it.  The segment of the EBDA is found at 40:000Eh, and the
amount of 'conventional' memory returned by int12h should be A000:0h
minus sizeof EBDA.  It is an additional scratch area whose fields are
ill defined and seem to be OEM bios specific.  It holds fields for the
mouse driver and mouse state, those are the most consistant, and other
fields used for the bios's benefit.  Originally, for the PS/2 line,
it's main purpose beyond the mouse was to hold information about the
hard drive geometry.

I would like to know if it is still present on the latest systems with
their USB everything, anybody know?

#dw40:0e
0040:000E 9FC0 C823 80F0 0002 2000 0000 002C 002C ..#...... ..,.,.

9FC0:0000h is correct for this system.

Steve

In article  <14a310ee-cffe-4b98-b8d5-4ce74c9f1229@i36g2000prf.googlegroups.com>
           spamtrap@crayne.org "junkoi " writes:

> Hi,
> 
> I am wondering if my option ROM can use Extended BIOS Data Area (EBDA)
> to store some (very) small data (around 16bytes)? Which area in EBDA
> is safe and guaranteed for my option ROM?
> 
> Do anybody know any updated documentation about EBDA?
> 
> Thanks,
> J

According to Peter Norton's PC Programmer's Bible (and cross- 
checked in RBIL) there is a "free for all" area of 16 bytes at 
address 40:00F0 to 40:00FF -- the Intra-Program Communications 
Area.

As anybody can use this (though I've never come across anyone 
other than me who did!) PN recommends that you include a checksum 
or signature there in order to have some confidence that the data 
you're reading back is yours...

Pete
-- 
   "We have not inherited the earth from our ancestors,
    we have borrowed it from our descendants."