Path: utzoo!utgpu!jarvis.csri.toronto.edu!rutgers!ukma!xanth!ames!sgi!key!perry
From: perry@key.COM (Peter Kiehtreiber)
Newsgroups: comp.sys.mac.programmer
Subject: Re: System 7.0 Q & A
Summary: Curious...
Keywords: Low Memory Globals
Message-ID: <811@key.COM>
Date: 18 May 89 00:28:28 GMT
References: <30353@apple.Apple.COM> <4666@okstate.UUCP> <1787@internal.Apple.COM> <7266@hoptoad.uucp> <13472@dartvax.Dartmouth.EDU> <7321@hoptoad.uucp> <30935@apple.Apple.COM>
Reply-To: perry@arkon.key.COM (Perry The Cynic)
Organization: Key Computer Laboratories, Fremont
Lines: 31

In article <30935@apple.Apple.COM> phil@Apple.COM (Phil Ronzone) writes:
> In article <7321@hoptoad.uucp> tim@hoptoad.UUCP (Tim Maroney) writes:
> >And all of these low memory locations can be trapped by the MMU and handled
> >transparently to the application.
> Well, that is not economical. When we launched a version of Lode Runner
> under A/UX, guess who was watching the clock ticks rather than using an
> A-line trap? (A/UX normally updates the ticks much less frequently).

After watching this line of discussion for a while, I can't keep still
any longer. Could somebody please explain to me WHY all the applications
in a Mac with PMMU have to share their low-memory globals? Why not give
each one a copy? (That's what the 2nd 'M' in PMMU is for, right? 'Mapping'?)

As for the system heap now, that's a more difficult problem. A possible
solution would be to split it into a 'clean' and a 'dirty' part; then share
the 'clean' (i.e., readonly) part and copy the 'dirty' part for each
application. Wastes some memory, but it's VIRTUAL memory now! Besides, even if
the entire system heap needs to be copied for each application, I'd be quite
willing to pay that price for protecting my applications from each other
(and from my own stupidity :-).

That leaves thingies like drivers that must muck around with the system's
data. But those critters can trash any operating system (ask any UNIX victim).

Puzzled and slightly confused mind wants to know. Flames by mail, real
information on the net, how's that sound? Thanks in advance
  -- perry
-- 
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Perry The Cynic (Peter Kiehtreiber)		     perry@arkon.key.com
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