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From: vrh@mhres.mh.nl (Michael Verhey)
Newsgroups: comp.sys.ibm.pc
Subject: Re: DOS memory allocation
Summary: Register usage for the appropriate DOS call
Keywords: fooling with DOS's mind
Message-ID: <3163@mhres.mh.nl>
Date: 17 May 89 06:12:20 GMT
References: <8261@phoenix.Princeton.EDU> <670@spudge.UUCP>
Organization: Multihouse NV, the Netherlands
Lines: 42

In article <670@spudge.UUCP>, johnm@spudge.UUCP (John Munsch) writes:
> In article <8261@phoenix.Princeton.EDU> jwbirdsa@phoenix.Princeton.EDU (James Webster Birdsall) writes:
> >                                                   It occurred to me
> >that an easy way to do this would to be allocate memory from the top
> >down instead of bottom up, as usual. Can DOS be persuaded to do this
> >in an elegant manner?
> 
> I'm sure you'll get tons of responses, but just in case...
> 
> DOS versions past 3.0 have the INT 21h function call 58h which sets the DOS
> memory allocation strategy.  One of the available options for this is to
> allocate from the top down.  Consult a DOS technical manual for details on
> the parameters of the function call.

You can use int 21h, function 58h as follows:

Calling registers:	AH = 58h
			AL = 00h, get strategy code
			     01h, set strategy code
			BX = Strategy code if setting it
			     00h, first fit (default)
			     01h, best fit
			     02h, last fit

Return registers:	Carry flag if cleared successful
			AX = Strategy code (if getting it)

			Carry flag set if error
			AX = Error code
			     01h, invalid function (file sharing)

By the way, I can highly recommend the book "DOS Programmer's Reference" by
Terry R. Dettmann (Que Corporation). It describes every BIOS and DOS call
available till DOS V3.3.

Good luck,
Michael
-- 
Michael Verheij (using Netnews)		Multihouse B.V., the Netherlands
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"Experience comes with the amount of equipment ruined."