From: Chris Holmes <cholmes AT surfsouth DOT com>
Newsgroups: comp.os.msdos.djgpp
Subject: Re: Question on Pointer
Date: Sun, 08 Aug 1999 13:27:18 -0400
Organization: Georgia Institute of Technology, Atlanta GA, USA
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To: djgpp AT delorie DOT com
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George Kinney wrote:
> 
> >>     I would like to convert an address into a segment and an offset,I know
> >> how to do it with Borland C (use of FTP_SEG and FP_OFF), but with djgpp I
> >> have not found how to do it
> >>
> >> Thanks

  Simple.  
  In protected mode, you have a selector and an offset.  The final 
address is simply selector + offset.
  In real mode, you have a segment and an offset.  The final address
is: segment * 16 + offset.  That's where the 1 meg limit came from 
(by multiplying the segment by 16 (or bit-shifting left by 4), that
gives
a 20 bit pointer, which makes the upward limit 1 meg (1 meg + 64K-15 if
you want to access some memory slightly over the top.  This was used
as a hack for years to access more than 1 meg in real mode).

  Chris

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