Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!tut.cis.ohio-state.edu!ukma!husc6!lownlab!kiely
From: kiely@lownlab.harvard.edu (James P. Kiely)
Newsgroups: comp.sys.ibm.pc
Subject: determination of free memory
Summary: How does one?
Keywords: PSP memory MicroSoft_C astart crt0.o
Message-ID: <1875@husc6.harvard.edu>
Date: 19 May 89 02:04:01 GMT
Sender: news@husc6.harvard.edu
Reply-To: kiely@lownlab.harvard.edu (James P. Kiely)
Organization: Lown Cardiovascular Laboratory, Harvard University
Lines: 38


I am trying to figure out how one determines how much memory
is available to a process, including that allocated to the process
and that which could be allocated with "setblock" (int 21, func 4Ah),
in DOS.  I have a number of questions:

1) What is the word at offset 2 of the PSP really?
According to Norton: ".. tells how much memory is available by listing
the segment-paragraph address of the end of DOS memory.  Multiplying
this number by 16 [decimal] gives the total bytes that DOS considers
usable.  The DOS command CHKDSK reports the same amount. ..."
After considerable finagling I have determined that this is the
"Total Memory" field of CHKDSK not the "Free Memory" field.
On my machine, an AT clone running PC-DOS 3.20, it is always A000h.
Is there an easy way to get the "Free Memory" field?

2) In every book I have ever seen, they are very emphatic that a user
process should not change any part of the PSP below offset 4Ch.
The startup code for MicroSoft C (crt0.o , astart:) modifies offset
2 of the PSP.  Why does MicroSoft C do this seemingly illegal behavior
and is it indeed illegal?  And what is the word at offset 2 of the PSP
after astart: modifies it?

3) What is the correct way to determine how much core is available to
a process?

4) What is the correct way to determine how much memory is available
in the far heap?

5) Is the far/near heap a DOS concept or a MicroSoft C concept?

Please respond via email.  I will summarize responses to the net.
Thanks.
=============================================================================
NAME:     James P. Kiely                USPS:   Kiely Laboratories
USENET:   ...!harvard!lownlab!kiely             P.O. Box 624
DOMAIN:   kiely@lownlab.harvard.edu             Allston, MA 02134-0624
PHONE:    +1 617 782 4136                       USA