Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!uunet!cbmvax!daveh
From: daveh@cbmvax.commodore.com (Dave Haynie)
Newsgroups: comp.sys.amiga
Subject: Re: Question about IBM and Multitasking: What is Micro channel?
Message-ID: <14257@cbmvax.commodore.com>
Date: 6 Sep 90 20:06:42 GMT
References: <1132@orange9.qtp.ufl.edu> <90246.143530UH2@psuvm.psu.edu>
Reply-To: daveh@cbmvax (Dave Haynie)
Distribution: na
Organization: Commodore, West Chester, PA
Lines: 33

In article <90246.143530UH2@psuvm.psu.edu> UH2@psuvm.psu.edu (Lee Sailer) writes:

>Zorro II and now III are the Amiga's equivalent standards.  MCA is an
>imporvement over ISA, but is incompatible with EISA and Zorro.  MCA and
>Zorro II have roughly equivalent capabilities.

Not exactly.  MCA is a full 32 bit bus that runs at 20MHz, while Zorro II
is a 16/24 bit bus that runs at 7.09-7.16MHz.  So MCA will greatly 
outperform Zorro II.  

Feature-wise, most of the basic features lacking in ISA, which drove IBM to 
adopt MCA, are in Zorro II.  These features include software configuration 
(ISA requires jumpers, versus Zorro II's AUTOCONFIG or MCA's POS), shared
interrupts (on ISA, only one card could use any particular interrupt line),
and multiple bus masters.

>                                              lee

>PS  I guess that offers the question, how hard would a Zorro <--> MCA
>    converter be?  Beats me.  8-)

It's certainly possible, but it could get a little ugly.  Zorro II, Zorro III,
and MCA handle certain fundamentals in very different ways.  The only reason
that Zorro III and Zorro II can coexist is that we were able to design a
reasonably complicated bus controller to inscribe Zorro II cycles within
Zorro III cycles, in a sense.  And of course, I did design Zorro III to 
coexist with properly designed Zorro II devices, but the way it's done is a
bit complicated.  At the least, you would lose a considerable amount of
performance going through an MCA bus converter.
-- 
Dave Haynie Commodore-Amiga (Amiga 3000) "The Crew That Never Rests"
   {uunet|pyramid|rutgers}!cbmvax!daveh      PLINK: hazy     BIX: hazy
      Get that coffee outta my face, put a Margarita in its place!