[WinMac] Comments on Microkernels [WAS: Re: Linux]

Dan Schwartz(expresso[at]snip.net)
Sat, 16 Jan 1999 14:57:12 -0500

        Hello!

        I'll thread my comments inline, since Chris H. made so many disparate (yet
quite salient and accurate) points.

At 09:47 AM 1/16/99 EST, Chris Hoogendyk, Network Specialist wrote:

        [cut]

>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.
>
>If LinuxPPC is faster than MkLinux then that is just because they did a
better
>job of porting Linux to the PowerPC.

        In the same vein, about 95% of NT is written in C... Only the lowest level
kernel services are platform-specific. That is why NT was originally ported
to 7 platforms (i860, i960, Alpha (AXP), PPC 6xx series (for IBM RS/6000),
MiPS, and x86).

        Now if only MS would re-port NT to the PPC 750 (G3) CPU, then we could run
it on iMacs... THAT would provide a REAL kick to Apple sales! :)

>
>You might think of it sort of like the comparison between RISC and CISC
chips.
>
>The implementation of the MacOS on PPC was extremely difficult because it is
>NOT a microkernal architecture. There were huge numbers of tool box routines
>that had to be converted and rewritten (and too small a team to do it). The
>magic bullet was when they found someone who was good enough to write the 68K
>emulator for the PPC. They did an unbelievable job of it (they had gone
>through several versions that were not good enough), and Apple stock soared
>when they delivered the first Power Macs. There is still code in the MacOS
>that is running in 68K emulation mode on a PowerPC. Each version of the MacOS
>gets a little more converted, and those parts that are converted run
>substantially faster.

        That is quite true: Michael "Diesel" Spindler, who was chief engineer on
the original PowerMac project came up with a bulletproof 68020 hardware
emulator in ROM with slow, but reliable toolbox routines. Then, as further
releases of System 7 software came out, these ROM toolbox routines got
flushed from RAM and were replaced with the code in the OS.

        HOWEVER, this technology for executing non-native code has been trumped by
FX!32 from DIGITAL. Read about it at:
 <http://www.digital.com/info/semiconductor/amt/fx32/>. For those of us who
are fortunate enough to use it (I was a beta tester for v1.0 almost 3 years
ago) FX!32 is an absolutely amazing code optimizer.

        [Cut]

>One of the reasons for Intel's constant load of backward compatibility in its
>chip architecture is that DOS and Windoze (following Dan's practice in
>distinguishing 3.1, 95, and 98) were, like the MacOS, not microkernal
>architectures, and rewriting them would not be economical. Note that DOS and
>Windoze do not run on Alpha or anything else.

        Thank G_d that DOS & windoze are isolated to the pee-cee toilet! :)

>
>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.

        Actually, IBM dropped it due to lack of sales; and internal politics more
than anything. Hell, IBM stopped the port of OS/2 to PowerPC as well...
Right in the middle of the big show in NYC!
>
>Chris Hoogendyk
>Network Specialist
>W.E.B. Du Bois Library
>UMass Amherst

        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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