Re: the thread on this forum about how to test if a diskette will
support a "media change line", I offer the following:

My system has an old 2007 single-CPU Biostar mainboard with a VIA
8237 controller (VIA has now just-about quit offering chipsets!).
My BIOS is from Phoenix and is dated 11-Jan-2007, as I can "read"
 from the addresses slightly beyond F000:0h, the start of my BIOS.

If I specify to the BIOS that my system has NO diskette, and then
boot from my hard-disk, byte 0:048Fh is set to zero.

If I then reconfigure the BIOS to use my diskette, then boot from
hard-disk, byte 0:048Fh is set to 001h, "change line supported".

I might also add, for the benefit of anyone at VirtualBox that is
interested in one MORE "bug", that on my system byte 0:048Fh does
NOT become 007h until the diskette READS something, i.e. the size
of the diskette (720K, 1.44-MB, or Japanese 2.88-MB) is left OPEN
until I actually USE the diskette!

Now, I ask you -- If Eric's and others' comments about using ONLY
the Int 13h calls (to determine diskette media-change capability)
are true, then WHY, in a BIOS dated as late as 11-Jan-2007, would
Phoenix find it NECESSARY to set byte 0:048Fh as they do??   BIOS
writers try to SAVE memory, even more than I do in UIDE, and they
don't give up code space in their ROM chips without good REASON!!

Add to that the data from BIOS Central (which I used to create my
caching driver in 2006); the VirtualBox source file Eric found in
which SOMEBODY at VirtualBox ALSO thought that byte 0:048Fh needs
to contain diskette media-change capability bits; and finally the
fact that, on actual "hardware" PCs, NOBODY has ever told me that
UIDE/UIDE2 have failed to cache diskettes properly, i.e. its code
for detecting and dealing-with diskette changes WORKS!

For all of the above REASONS, I shall again REFUSE to update UIDE
and UIDE2 to use any more Int 13h requests.   In the "real world"
(NOT the "VirtualBox" world), UIDE/UIDE2 run fine, and I now have
enough EVIDENCE of my own to indicate there is NOTHING wrong with
the CHOICE that I made in 2006 to use byte 0:048Fh's data instead
of Int 13h calls.   VirtualBox needs to get FIXED; END of story!!

I do not know when/why having byte 0:048Fh denote diskette media-
change capability was added to the BIOS.   But, I bet that if any
of you ask Phoenix and other BIOS vendors if Int 13h is "the only
way" to test such capability, they may just have REASONS to laugh
your sorry [rear-ends] out-of-town!   What they provide as a real
world "For SALE!" product takes PRECEDENCE, in my mind, over some
rather archaic "IBM AT" BIOS specification!

Live Security Virtual Conference
Exclusive live event will cover all the ways today's security and 
threat landscape has changed and how IT managers can respond. Discussions 
will include endpoint security, mobile security and the latest in malware 
Freedos-user mailing list

Reply via email to