Path: utzoo!mnetor!uunet!husc6!think!ames!lll-lcc!pyramid!voder!apple!goldman
From: goldman@Apple.COM (Phil Goldman)
Newsgroups: comp.sys.mac.programmer
Subject: Re: MultiFinder and TopMem() question
Message-ID: <7668@apple.Apple.Com>
Date: 14 Mar 88 06:02:03 GMT
References: <730008@hpcilzb.HP.COM>
Reply-To: goldman@apple.UUCP (Phil Goldman)
Organization: Apple Computer Inc, Cupertino, CA
Lines: 46

In article <730008@hpcilzb.HP.COM> tedj@hpcilzb.HP.COM (Ted Johnson) writes:
>
>What is the proper way to check for the total amount of
>RAM?  Under 4.1/5.5 the following works:
>
>	long totalRAM;
>
>		totalRAM = (long)TopMem()/1024;
>
>But under MultiFinder this gives me too small a number (i.e., 179 
>instead of 1024).

MultiFinder changes low memory variable MemTop (accesses by routine TopMem())
to a number *approximately* equal to the size of system heap + the size of
the current (i.e. calling) application's partition.  The rationale behind this
is to "convince" older apps that this is the size of the machine.  Note that
this changes MemTop to be a size rather than a pointer; the 2 were equivalent
before because RAM starts at 0, but most apps used it as a size.

Hopefully an application does not need to know the real value of MemTop, or
even a fake one, but if it does it should only need it for purposes of
displaying machine information.

Anyway...it seems that we were remiss in the first release of the MultiFinder
Development Package.  There *is* a MF temp memory call for MemTop, as follows:

/* MultiFinder dispatch trap */
#define OSDISPATCH				0xA88F

/* Routine selector value */
#define mfMemTopSel				22

/* Macro that the gets put into your source code */
#define MFMemTop() \
cTWMemTop(mfMemTopSel)

/* And the actual trap that gets called */
pascal Ptr cMFMemTop(SW)
   short		SW;
   extern OSDISPATCH;
			
This info will be put in the MultiFinder documentation ASAP, along with the
corresponding interfaces for Pascal and assembler.

-Phil Goldman
Apple Computer