Re: How to protect 65816's 16MB Memory?

[salfter@salfter.diespammersdie.dyndns.org (Scott Alfter)]

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In article <MPxOd.46134$iC4.31797@newssvr30.news.prodigy.com>,
Bryan Parkoff <nospam@nospam.com> wrote:
>    It looks like that Apple IIgs uses real mode, but it does not have 
>protected mode.  What happen if you access "Visit Monitor" in Control Panel 
>while GS/OS 6.0.1 is running after you zero in some memory pages?  GS/OS 
>will crash!!  Do you have idea why it does not have protected mode feature 
>in 65816 CPU like 80x86 CPU?

You answered your own question...the processor doesn't implement paging or
any sort of memory protection.  The x86 and 680x0 processors in common use
in 1986 didn't offer this capability, either (though there were external
PMMUs for at least the 68020, and they worked in some of the '020 Macs).

>    Someone mentioned that GS/OS has its own memory manager to handle 
>memory, but assembly programmers have an ability to overwrite memory pages.

All the memory manager can do is allocate chunks of memory to one program or
another...and since you can have only one program running at a time anyway
(excluding DAs from consideration here), there's probably not even much
point in that.

Expecting modern features to be present in nearly-20-year-old hardware is
insane.  You can sometimes add this stuff in later on, but hardware-based
memory protection wasn't something you'd see on PCs in the mid-'80s.

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