At  6:37 PM 12/16/93 -0500, Allen X Briggs wrote:
>> (1) Wouldn't it be easier to make a version of MacBSD that runs on *top* of
>> the Mac OS?
>
>No.  MachTen, MachMac, and MacMach all use the MacOS to varying extents.
>The obvious advantage is that you get compatibility pretty much across the
>board, as accesses to the hardware are done by the MacOS.  The MacOS,
>however, is hardly designed to multitask.  It's not designed with a lick of
>memory _protection_.  The whole bloody thing runs in "supervisor" mode
>instead of "user" mode...

Professional MachTen models BSD Unix exactly:  MachTen applications run in
user mode and the MachTen kernel runs in supervisor mode.  So, there is
protection for Unix and Mach applications running under Professional
MachTen. True MacOS has no protection and we do run the Macintosh
applications in supervisor mode, but this is no different than a Macintosh
without MachTen.

Personal MachTen (the equivalent of Brian Kendig's vision of a MacBSD Lite)
does run in supervisor mode, sacrificing protection, but gaining the
ability to run on all Macs, e.g., SE, Classic, etc.

With either flavor of MachTen the operation is much like that of
co-resident operating systems, with the Mach kernel and MacOS sharing the
processor.  When MachTen has control of the processor, it pre-emptively
multitasks Mach/Unix applications and when MacOS has control, it lets
Macintosh applications run in their normal cooperative sharing mode.

>We are more interested in running Unix than running Mac, ..

For people more interested in running Unix than Mac, you can run
Professional MachTen without running Finder; this eliminates the
possibility of misbehaved Mac applications crashing your machine.  Most
users however are happy to have both Unix and Mac applications running
simultaneously.

>>What's keeping MacBSD from being able to run on old 68000 Macs?

>Unix is a multitasking OS,..

Virtual memory is not necessarily needed for multitasking.  Since Personal
MachTen runs in real memory and doesn't have to take page faults, it
provides more performance than you would expect. And, for applications like
communications (using your Mac as an Internet host, mail server, domain
name server, print server, gateway, etc.), rather than general purpose
programming, it is actually perferred over Professional MachTen.

Sorry we missed the pizza party...

Best regards,
Anita





Tenon Intersystems
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Santa Barbara, CA 93101
805-963-6983
FAX: 805-962-8202
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