🚀 go-pugleaf

In article <1132@watserv1.waterloo.edu> ssingh@watserv1.waterloo.edu ($anjay "lock-on" $ingh - Indy Studies) writes:
$I was wondering about the competing bus standards, EISA and Micro Channel.
$Not being too familiar with PC architectures yet (my last machine was a 64)
$I was wondering if someone could explain what this means for PC board
$performance for peripherals and CPU throughput. 

   Just to make sure we're straight here, EISA and MicroChannel are both
I/O bus designs, and have nothing to do with the main processor (unless
the board you're plugging in is an expansion memory board).

   Now for some history.  The original PC bus was 8 bits wide, since the
8088 appears to be an 8-bit processor to the outside world.  When the
AT came along, using the 80286 with a 16-bit interface, the PC bus was
expanded to 16 bits.  This is referred to as ISA, for Industry Standard
Architecture, and is what you'll find in most 386SX machines (and until
EISA came along, most 386DX machines use simple extensions to it).

   When IBM designed the PS/2 family, they figured they'd had enough of
other companies building clones, so they designed a new bus.  Well, that's
a bit jaded ... the MicroChannel supposedly is designed for multiple bus
masters and has some other nifty features to improve throughput, but IBM
also wanted to try to do away with a lot of the competition.  MicroChannel
is not compatible with ISA ... it uses different sized cards, different
sized connectors, and has a whole pile of different signals.

   Seeing what IBM was doing, a group of (nine, I think) companies got
together to propose an enhancement to ISA, called EISA, which would be
compatible with all the old ISA cards and also provide a high-speed
standard for 32-bit I/O boards as well.

   Which is better?  It depends on who you listen to.  In any case,
the theoretical capabilities of each bus exceed the level of current
I/O cards (I think they both have burst transfer rates of around 40
MB/s, for example), so there isn't really a performance advantage to
one or to the other.  Personally, I'd stick with EISA for a few reasons:

- for any function that exists on an expansion card, you'll find it on
  an ISA card but not necessarily on a MC card

- ISA/EISA cards are cheaper to design and produce than MC cards, since
  MC cards are a _lot_ smaller and virtually require surface-mount
  technology and custom VLSI chips so that you can fit everything on
  a board.  This was a move on IBM's part to help ensure that they'd
  have less competition.

- if you're upgrading an old PC, your old cards will still work in an
  ISA/EISA machine, whereas to go MC you'll have to replace them _all_.

   I guess I should state that all anti-IBM opinions here are strictly
my own, though a lot of people would agree with them :-)
-- 
Stephen M. Dunn                               cs4g6ag@maccs.dcss.mcmaster.ca
          <std_disclaimer.h> = "\nI'm only an undergraduate!!!\n";
****************************************************************************
               I Think I'm Going Bald - Caress of Steel, Rush