Re: Is there a limit....... (and a DTUtils progress report)

[amorton@ee.mu.OZ.AU (Anthony Morton)]

In article <2k6i6m$kh9@senator-bedfellow.MIT.EDU> pbauer@ATHENA.MIT.EDU (Paul H Bauer) writes:
>	Is there a limit to the number of inits and DAs that one can have 
>installed and active on a GS assuming 4 meg of RAM? If there is a limit 
>is this caused by limited RAM or limited address space in certain areas of
>memory? I am trying to understand the cause of a GS/OS System Error =$0043.
>
>pbauer@mit.edu

Normally, every DA and init you have installed in your system takes up a
certain amount of RAM.  A typical init or DA is loaded, in its entirety, into
RAM at startup time and remains there until shutdown.  Many newer DAs have
resource forks and/or dynamic segments which are loaded only when needed, so
that they don't take up so much RAM space when not in use.  Still, there is
always an upper limit to the number of DAs/inits you can have installed,
although this is reasonably large on a 4 meg system.  In addition, most DAs
and inits like to be installed in 'non-special' memory, thus excluding 256K of
RAM which is nevertheless a fairly small proportion of the total.

%begin(sales_pitch)

Rob Mueller and I devised a solution to this problem some time ago, which we
call the 'Virtual DA' concept.  (If you've heard this all before, please skip
this paragraph.)  The basic idea is to install an 'empty' DA into the system
(which takes up very little RAM space), which contains nothing but the header
and instructions to jump to a Virtual DA loader; this then loads the real DA
from disk and opens it.  After the DA is closed, it is unloaded, leaving the
empty DA in memory.  Our program Desktop Utilities contains a facility for
managing Virtual DAs, which appears to be the only one of its kind.  It also
allows you to add inits 'on the fly' as IR does; note however that many inits
do not like being installed other than at startup time.

Rob and I have been working on a total rewrite of Desktop Utilities for some
time now (make that a long long time :-).  Our 'alpha' version now has a
working NDA kernel, a menu bar clock that can be moved off the menu bar and
stuck onto the desktop, and most importantly here, a working, greatly improved
Virtual DA Manager, which overcomes some shortcomings of the present release
(version 3.3) and includes some major enhancements to the user interface
(most notably, changes to the installation take effect immediately).  We are
considering making this part of DTUtils 4.0 available as a preliminary release.

If you'd like more information, please reply via EMail.  (My account at
Melbourne Uni has just reopened after being off the air for three months!)

Hope this helps,

Tony Morton (amorton@ee.mu.oz.au)
Electrical Engineering Masters student & diehard IIGS lover