Date: Mon, 18 Dec 2000 09:59:05 +0000 From: Matthew Seaman <m.seaman@inpharmatica.co.uk> To: Jordan Hubbard <jkh@winston.osd.bsdi.com> Cc: Andrew Reilly <areilly@bigpond.net.au>, Patryk Zadarnowski <pat@jantar.org>, Tony Finch <dot@dotat.at>, SteveB <admin@bsdfan.cncdsl.com>, freebsd-hackers@FreeBSD.ORG Subject: Re: kernel type Message-ID: <3A3DDFE9.5AD693B6@inpharmatica.co.uk> References: <6134.977051878@winston.osd.bsdi.com>
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Jordan Hubbard wrote:
>
> > Yeah, but in what sense is that use of Mach a serious
> > microkernel, if it's only got one server: BSD? I've never
> > understood the point of that sort of use. It makes sense for a
> > QNX or GNU/Hurd or minix or Amoeba style of architecture, but
> > how does Mach help Apple, instead of using the bottom half of
> > BSD as well as the top half?
>
> That's actually a much better question and one I can't really answer.
>
> One theory might be that the NeXT people were simply Microkernel
> bigots for no particularly well-justified reason and that is simply
> that. Another theory might be that they were able to deal with the
> machine-dependent parts of Mach far more easily given its
> comparatively minimalist design and given their pre-existing expertise
> with it. Another theory, sort of related to the previous one, is that
> Apple has some sort of plans for the future which they're not
> currently sharing where Mach plays some unique role.
As I remember, way back in the mists of 1990 when I first encountered a NeXT
box, one of the principal reasons for selecting the Mach 2.x micro kernel was
"mach messaging". This was a unified mechanism for almost all IPC both within
one host or distributed over a network, where eg. sockets (netork or unix
domain), pipes etc. were seen as abstractions of the core messaging function.
This fitted very well with the general OO design philosophy of the company.
If anyone has access to a copy of the socket(2) man page from any NeXTSTEP
version, I dimly remember there being an informative paragraph about this
point.
Whilst Mach messaging was not commonly used directly in the Unix userland
which was pretty much stock BSD 4.3, it was very important in the AppKit ---
NeXT's real stock in trade.
Matthew
--
Certe, Toto, sentio nos in Kansate non iam adesse.
Dr. Matthew Seaman, Inpharmatica Ltd, 60 Charlotte St, London, W1T 2NU
Tel: +44 20 7631 4644 x229 Fax: +44 20 7631 4844
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