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From: dcr0801%ritcv@cs.rit.edu
Newsgroups: comp.unix.i386
Subject: Memory Access over the 1Meg. boundry
Message-ID: <1439@cs.rit.edu>
Date: 13 Dec 89 19:30:21 GMT
Sender: news@cs.rit.edu
Reply-To: dcr0801%ucss@cs.rit.edu ()
Distribution: usa
Organization: Rochester Institute of Technology, Rochester, NY
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I am currently writing my own little *nix type OS on a IBM type machine.
The hardware has 1 meg. on the system board, and 512k in an expansion
I/O slot.  Currently running the processor in 286 mode, any descriptor
table entries where the base address is over the 1 meg boundry gets 
truncated to the lower meg.  This gives me only 640k of usable memory.  
I am sure (99%) that my tables entries are correct, yet I still can't 
access the 'expanded' memory.  Is there some kind of bit somewhere that 
enables the processor to generate address over 20 bits on the address bus??
I could only guess that DOS (yeck!) does something to map higher memory 
into lower memory so that it could be access in real mode.  I know that 
there must be a way to be able to just generate the 24 bit address and get
the memory without mapping it, but, like I said, I haven't found the 
'Golden Bit' yet.  If anyone out there in net.land could give me a little
hint on this, it would be GREATLY apprieciated!!  
Thanks in Advance,
   Dave Rein

(dcr0801%ucss@cs.rit.edu) or (..!uunet.uu.net!ultb.cs.rit.edu!ritcv!dcr0801)

 [Sorry, no cute byeline at the moment.  Hard to be funny and frustrated!!]