Re: [WinMac] Re: Linux

CHoogendyk@AOL.com
Sat, 16 Jan 1999 09:47:16 EST

>>"LinuxPPC runs "natively" on PowerPC computers, rather than relying
>>on the Mach microkernel, as MkLinux and Rhapsody do. As a result,
>>LinuxPPC is about 20% faster than any microkernel-based offerings.
>>LinuxPPC enjoys better stability and device support than MkLinux.
>>For example, the floppy drive works in LinuxPPC."
>
>But does it offer protected memory and "true" multitasking like MKLinux
>is supposed to?? I haven't played around too much with either but would
>like to (as soon as I get some time).

(If it doesn't offer those things, then it is not Unix or Linux.)

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.

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.

The OS from NeXt had a real advantage because it WAS a microkernal
architecture. Rhapsody was the code name for the OS that was to meld the MacOS
interface with the NeXt OS microkernal and other services and utilities and
also include the Mac toolbox in a way that would allow developers to not have
to scrap everything. This is very soon to be out as MacOS X Server (see
www.apple.com). Steve (and many major developers, such as Adobe) felt that it
didn't go far enough. Steve pushed the Apple staff harder and came up with
MacOS X which will not require developers to do substantial rewrites as
Rhapsody would have. This will be out later this year.

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.

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.

Chris Hoogendyk
Network Specialist
W.E.B. Du Bois Library
UMass Amherst

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This archive was generated by hypermail 2.0b2 on Sat Jan 16 1999 - 06:50:49 PST