Path: utzoo!utgpu!water!watmath!clyde!rutgers!rochester!cornell!batcomputer!pyramid!voder!apple!goldman
From: goldman@apple.UUCP (Phil Goldman)
Newsgroups: comp.sys.mac
Subject: Re: Boot Blocks
Message-ID: <6983@apple.UUCP>
Date: 14 Dec 87 17:18:51 GMT
References: <36343@sun.uucp>
Reply-To: goldman@apple.UUCP (Phil Goldman)
Organization: Apple Computer Inc., Cupertino, USA
Lines: 34

In article <36343@sun.uucp> chuq@plaid.Sun.COM (Chuq Von Rospach) writes:
>1) How can I find out what the System Heap numbers in the boot blocks are
>   set for?
>
>The reason I ask is that I believe most of the glitchies I've seen since
>the upgrade to system 5.0 and multifinder are system heap exhaustion
>problems. I read somewhere that the heap grew again (implying that the boot
>block numbers got bigger) for Multifinder. But I can't find any program that
>reads the blocks or writes the blocks or any documentation on what they
>should be. 
>

INIT 31 will guarantee that there is some minimum amount of memory free in the
system heap (16k currently, I believe) before the startup application is
launched and the system heap is resized dynamically under MultiFinder.
Therefore, the number in the boot blocks has very little meaning; it only
needs to be big enough to get the system up and going.

There reason for the system heap "exhaustion" under MultiFinder occurs because
there are certain cases when it is just not possible for MF to grow the sys
heap "on the fly."  The most obvious instance of this is when all of available
memory is in use.  However, it can also happen when the last application
launched was forced to load into a relatively low memory address.  Since the
memory for this application cannot be moved, it provides a ceiling for the
growth of the sys heap.  Therefore, quitting other apps will not alleviate the
problem (which shows up most frequently as the inability to open a DA but
might cause a crash in extreme conditions), only quiting this particular app
will.

We are actively pursuing methods for making the memory for running applications
more relocatable.

-Phil Goldman
Apple Computer