From:	Dave Bird <dave AT xemu DOT demon DOT co DOT uk>
Newsgroups:	comp.os.msdos.djgpp
Subject:	Re: DPMI-Alloc with 192MB RAM - how ?
Date:	Mon, 26 Jul 1999 01:12:56 +0100
Organization:	ARS HakeMongers inc...... ><_'> <_"
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References:	<Pine DOT SUN DOT 3 DOT 91 DOT 990722195834 DOT 29776A-100000 AT is>
	<7n7si0$ae1$1 AT news DOT luth DOT se> <3797dc74 DOT sandmann AT clio DOT rice DOT edu>
	<7n9gpq$5lf$1 AT antares DOT lu DOT erisoft DOT se> <3798d38d DOT sandmann AT clio DOT rice DOT edu>
	<7nepsn$34o$3 AT news DOT luth DOT se> <379b8e09 DOT sandmann AT clio DOT rice DOT edu>
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In article <379b8e09 DOT sandmann AT clio DOT rice DOT edu>, Charles Sandmann
<sandmann AT clio DOT rice DOT edu> writes
>> Charles Sandmann (sandmann AT clio DOT rice DOT edu) wrote:
>> : In r5 the maximum will be 2Gb which would consume an extra 64Kb.  Dos memory 
>is
>> : a precious resource which is needed for DMA buffers, nested images, and 
>> : pagetables.  The number of users which needed more than 128Mb of virtual 
>> : is very small ...
>> 
>> Are you saying this extra 64KB (or 4KB) is needed for every nested
>> program?
>
>No, only once for the DPMI provider.  But page tables for large memory is 
>a big problem.  It takes 4Kb for each 4Mb memory address space you have 
>touched.  So, if you want to use 384Mb physical memory (no virtual) then
>you need 384Kb of memory just for the page tables.  With DOS needs, DJGPP
>low memory needs, and other DPMI needs - you can't afford to just waste
>any of it.  Some very small memory machines (640K/1Mb total memory 386s) 
>are supported by CWSDPMI - and it must use DOS memory for all purposes.


 Charles, couldn't the program either (1) suggest a default supported 
 size based on knowing how much DOS memory there is, or (2) simply be
 recompilable with options for different large memory configurations?
 Then everyone would be happy.


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