[WinMac] NT portability [WAS: Re: Linux]

Dan Schwartz(expresso[at]snip.net)
Sun, 17 Jan 1999 10:40:41 -0500

        Good morning!

        For clarity, Danny Thomas is ">" & Chris H is ">>"

At 10:38 PM 1/17/99 +1000, Danny Thomas wrote:
>CHoogendyk@aol.com replied
>
>>Actually, it's my understanding that it is the microkernal architecture of
>>Unix that makes it so portable. The C code for lots of stuff (like Sendmail)
>>is pretty general and simply has to be recompiled on the target machine. The
>>real work is in recoding the microkernal. Once that is done, the rest is
>>relatively easy. I believe the Mach microkernal is just a rewrite of the
Unix
>>microkernal by folks at Carnegie Mellon that NeXt bought the rights to use.
>I know this is off-course, but UNIX does NOT use a microkernel.

        [cut to near bottom]

>MacOS was never written with portability in mind.

        Wasn't the CHRP/PPCP fiasco a sort of portability?!
>
>>Windows NT has some element of the Microkernal concept built into it.
This is
>>why they were able to develop NT for Alpha and PPC. It wasn't, however,
>>terribly easy because Microsoft made things more complicated than necessary.
>>IBM eventually dropped the NT on PPC project.

        According to (again!) Sean Daily's "Optimizing Windows NT reference book,
only about 15-20% of NT is CPU-specific... The balance of NT is written in
"C."

>at one point MS were talking of NT being microkernel-like. I believe NT was
>derived from Dave Cutle's work at Digital which was a true micro-kernel. NT
>has a monolithic kernel, eg for performance reasons, the video drivers were
>moved into kernel address space for NT4, so any driver bug could bring the
>whole system down.

        Also, and very importantly, the Printer service and Server service were
moved from Ring 3 in NT 3.51 to Ring 0 in NT4; so any bugs there will also
bring down an NT system. The reason for moving the Server engine down to
Ring 0 was to directly compete with NetWare 4.1: Novell (correctly)
advertised that NetWare 4.1 was about twice as fast as NT/Server 3.51 on
the same machine; and moving the Server engine from user (protected) mode
to kernel mode essentially doubled the server speed, and closed the gap.

        [As a side note, *I think* the "Daytona" server engine in NT 3.5 ran in
Ring 0. (Corrections welcomed)]

>In spite of the conspiracies some people like to believe in, I think the
>main reason for NT being dropped on non-Intel architectures were primarily
>commercial. Of course NT/Alpha continues, but DEC put a lot of resources
>into this right from the early days of NT. As one example of the commercial
>pressures, at one point MS was supplying a version of Office for the then
>available copy of NT on MIPS platforms (eg SGI). That got dropped when they
>sold less than 10 copies in one year.

        I can't comment about the MIPS situation, because I don't know about the
politics; but for the PowerPC platform IBM basically killed their half of
the support, and MS reciprocated. (Remember the war between MS and IBM over
OS/2?!)

        The DIGITAL/MS alliance for the Alpha port was very strong, although it
got a bit shaky in the early days of the Compaq buyout. However, as far as
I can determine, this (Alpha) support has actually been increased as of
late. "Shannon Knows DEC," err, "Shannon Knows Compaq" has more info on
those politics

>
>cheers,
>Danny Thomas

        Yours truly,
        Daniel L. Schwartz,
        Electrical Engineer.

        Dan's Macintosh Consulting
        Suite 1306
        1840 Frontage Road
        Cherry Hill, NJ 08034-2205

        609-795-8965

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