Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!wuarchive!zaphod.mps.ohio-state.edu!sdd.hp.com!elroy.jpl.nasa.gov!jarthur!nntp-server.caltech.edu!tybalt.caltech.edu!toddpw
From: toddpw@tybalt.caltech.edu (Todd P. Whitesel)
Newsgroups: comp.sys.apple2
Subject: Re: GS/OS et al
Message-ID: <1990Oct17.014216.14617@nntp-server.caltech.edu>
Date: 17 Oct 90 01:42:16 GMT
References: <0093E3490C99F300.00000111@dcs.simpact.com>
Sender: news@nntp-server.caltech.edu
Organization: California Institute of Technology, Pasadena
Lines: 21
Nntp-Posting-Host: tybalt.caltech.edu

whitewolf@gnh-starport.cts.com (Tae Song) writes:

>Huh, what?!?  The 65816 can only address 24-bits directly.  In the GS, Apple
>limited that to half which is 23-bits.  24-bits is 16M and 23 is 8Ms.
>Just how did you manage to get 4 GigaByte???

Simple. GS Applications are required to treat any pointer value as a 32 bit
quantity, with the memory available to the current hardware starting at 0.
The hardware can only access 24 bits / 16 megs but applications that follow
Apple's guidelines (plus some of the tools will barf on non-zero high bytes)
will still work if the high byte ever becomes significant. The Mac O/S did
not formally place this restriction on applications until the '32 bit clean'
coding standard was introduced, and any program that doesn't obey it will
break under system 7.

In this sense, GS/OS is a 32 bit / 4 gig operating system although there are
plenty of instances where user code would break if it were located at a true
four byte address.

Todd Whitesel
toddpw @ tybalt.caltech.edu