Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!asuvax!noao!ncar!gatech!mcnc!ncsuvx!news
From: bank@lea.ncsu.edu (Dave The DM)
Newsgroups: comp.sys.ibm.ps2.hardware
Subject: Re: Micro Channel Bus Extender/Protoboard
Message-ID: <1990Oct13.052355.17374@ncsuvx.ncsu.edu>
Date: 13 Oct 90 05:23:55 GMT
References: <15104@hydra.gatech.EDU>
Organization: Leazar Hall MicroVax II (CSCLEA), NCSU, Raleigh NC
Lines: 28


    The problem with using MCA in the setting you desire is the
radical change in bus design between it and ISA.

    ISA had little in the way of bus arbitration. A card on the bus
would, in many cases, simply assert the bus request line and hold it
until the controller responded. Device arbitration is virtually
non-existent...whoever gets there first wins.

    MCA, on the other hand, maintains relatively rigid control
over the bus. The machine knows what devices are where, how many
slots it has, and so forth. The bus controller uses all of this 
information to arbitrate the bus. 

    Ergo, it is very difficult to extend the MCA bus. I do know os
(of) a box that, thru black magic and witchery, can do so...it was
reviewed a number of months ago in PC Magazine. It can only
extend the MCA bus by using ISA cards, and you must inform the
MCA bus machine os the location and identity of each and every ISA
card in the external bus. PC Magazine concluded that for the price
(in excess of three digits) it was better to get an MCA machine with
more slots.

    In short, I'd suggest that you stick to ISA. If you want to
add the concept of "real" bus arbitration and other goodies, try
EISA. 
 
                           Dave The DM