Hi,

> Could someone enlighten me in the subtly differences / similarities /
> relations of the PREP / CHRP / ofppc / macppc architectures please?

While I have to admit that I don't know much aboutspecific models
of Macs or IBM ppc boxes, eespecially not the newer ones, I may be able
to give a short note about the various ppc architectures.

When the ppc alliance between Apple, IBM and Motorola was formed, there
was an effort to define a reference platform which would allow to run
various OSs (at that time, there was talk about Windows NT, OS/2, AIX,
Solaris, Taligent (some experimental OS that never saw the light of day)
and of course MacOS) on the same machine.  The result of this was the PReP
specification.  Unfortunately, Apple wasn't too eager to support this
and stepped out of this effort quite early, developping its own boxes
based on the processor.  The other participants in the alliance as well
as some third parties did produce boxes that complied to the PReP
specification (albeit there were quite some boxes delivered after
June 1995 without OpenFirmware; see next paragraph), but without too
much commercial success.

Regarding OpenFirmware, the PReP specification, while letting early
adopters time for migration, required that a compliant machine had to
implement it on boxes delivered after June 1, 1995.

In 1995, shortly before Jobs returned there, Apple became a bit more open
and, together with IBM and Motorola, started a new effort to merge the
different architectures, the CHRP specification.  As an aside, at the same
time, Apple released specifications to their older machines to some clone
manufacturers, who produced a few boxes accordings to these specs.

This CHRP specification requires the implementation of OpenFirmware plus
some additional interface to allow an OS access to the hardware without
specific drivers in the OS itself, the RTAS.

Again, there were a few CHRP compliant boxes by IBM and Motorola and
some third parties.

After the return of Jobs, Apple became rather closed again and the support
for open specifications returned to a minimum.  In fact, I was quite surprised
when I learnt that Apple had released some CHRP comliant boxes at all, albeit
quite some years later.  As mentioned above, I don't know next to nothing
about any newer boxes they make.

NetBSD/ofppc is an effort to support any PowerPC box implementing a complete
OpenFirmware, especially including the OpenFirmware Client Interface.
The OpenFirmware is used for any access to the hardware, so the OS doesn't
have to have specific drivers for any device.  Of course, as devices are
accessed by interpreted code this way, any hardware access is relatively
slow compared to using native drivers.

> Reason for this questions: I will get an IBM RS/6000 7046-B50 next
> weekend. It looks like this is a CHRP machine with OpenFirmware and now
> I try to find the proper NetBSD port for it.
> http://www.netbsd.org/Ports/prep/ says:
> NetBSD/prep is the port of NetBSD to early PReP (PowerPC Reference
> Platform) machines.
> No CHRP?
> But http://www.de.netbsd.org/Ports/ says:
> prep powerpc  PReP (PowerPC Reference Platform) and CHRP machines
> So I asume the PREP port is the right place to start?

Hmm, albeit I don't know too much about these boxes, I'd indeed look
at NetBSD/prep first.

> And where can I get docs about CHRP? The link to the PREP specifications
>   ftp://ftp.austin.ibm.com/pub/technology/spec/ on the port-prep
> homepage is dead. I googled, but found nothing but dead liks.

Hmm, some searching around on the net revealed
ftp://ftp.software.ibm.com/rs6000/technology/spec/ and
ftp://ftp.software.ibm.com/rs6000/technology/spec/chrp/ where you
may find what you are looking for.

Hope it helps.

Ciao,
Wolfgang
-- 
ws@TooLs.DE     Wolfgang Solfrank, TooLs GmbH 	+49-228-985800