Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!usc!julius.cs.uiuc.edu!apple!netcom!mojo
From: mojo@netcom.UUCP (Morris Jones)
Newsgroups: comp.windows.ms.programmer
Subject: Re: 386 Enhanced Question
Keywords: Memory 386 Protected mode
Message-ID: <19202@netcom.UUCP>
Date: 20 Dec 90 22:55:42 GMT
References: <4566@media-lab.MEDIA.MIT.EDU>
Organization: Netcom- The Bay Area's Public Access Unix System {408 241-9760 guest}
Lines: 26

jason@media-lab.MEDIA.MIT.EDU (Jason A. Kinchen) writes:
>When the documentation says that you have a 4 Gig address space in 386
>Enhanced mode, how's it doing that?  The MS C compiler is only making
>16 bit code and not using the 32 bit segment registers on the 386, so
>what gives?  I guess the Windows Global heap might be using a 32 bit
>register, but how's it getting a 32 bit pointer back into the MS C
>compiled application?

Yes the MS C compiler is making 16-bit code.  Windows all runs in 16-bit
code segments.  But each of those segments can be up to 64K in size, and
you can have LOTS of them.  So you can actually use 4 Gig of address space.

Remember that on the 386 you don't have a segment number, you have a Selector
(or Descriptor).  This number is not a memory reference, but an index
into a table which describes the physical memory address being used.  Thus
a 16:16 pointer can refer to any address in the physical (or virtual)
address space.  You can use all of memory with 16:16 pointers in
selector:offset form.

Mojo

-- 
mojo@netcom.UUCP          Site Coordinating Instructor, San Jose South
Morris "Mojo" Jones       Skilled Motorcycling And Rider Training (S.M.A.R.T.)
Campbell, CA              800-675-5559 ... 800-CC-RIDER ...  408-423-2212
AA4KB @ N6LDL.#NOCAL.CA.USA.NA / aa4kb.ampr.org / netcom!mojo@apple.com