From: Don <north_@www.7f.no-ip.com>
To: 9fans@cse.psu.edu
Subject: [9fans] Random Question
Date: Tue, 21 May 2002 08:47:40 +0000 [thread overview]
Message-ID: <8f6cf824.0205201813.34db153f@posting.google.com> (raw)
Heyas,
I just finished writing most of the MBR
for my Autumn OS and began reading through FS
documentation to help me develop my FS. Now.. an
intereting notion crossed my mind while reading
the FAT specification by Microsoft. If byte zero
of a BPB jmp_Boot is 0xEB (the preference is this
short jmp according to the specs) the third byte
_must_ be a NOP (0x90). Now, I remember reading
in several other operating system's comments
that some BIOS actually bail out if there isn't
a jmp short followed by a nop in the first three
bytes of code. Noone seemed to know why the
BIOS needed to see that nop there. Could this
have been a tactic used by Microsoft to attempt
to thwart other Operating Systems from occupying
an IBM PC? I mean, if the BIOS is designed to check
for a documented FAT specification, wouldn't that
be a clue that Microsoft coerced the manufacturers
to implement the check? Anyone out there have a
comment on this issue?
Don
next reply other threads:[~2002-05-21 8:47 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2002-05-21 8:47 Don [this message]
2002-05-21 10:05 ` greg andruk
2002-05-22 8:52 ` Don
2014-07-03 11:44 [9fans] random question Nick Owens
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