Subject: ISA or not? (Was: Re: Long ramblings about project design)

From: [email-masked] (Tor Arntsen)
Date: Fri, 25 Jun 1993 13:21:43 +0200

Drew Eckhardt wrote:
[...] 
} I'm begining to wonder about the need for the ISA bus - 
I'm beginning to wonder as well.. 

} 
} Pros : we can put nifty things like ROM burners in the ISA slots, and
} 	parallel printer/floppy controllers.
What about RS-232 ROM burners?  I have to admit I haven't used ROM burners 
since when one could only get serial versions.  Are ISA versions more useful?

} Cons :  the ISA slots take up lots of realestate (not just 
} 	for the connector - we could have clearance problems with 
} 	heat sinked chipps and SIMMs)
} 
} 	Interfacing the ISA bus to the MIPs could be complicated,
} 	since the existing bus interface chips are designed to 
} 	mate up with x86 CPUs, etc.
 
I need Video, Ethernet, SCSI, serial (in that order of preference :-)
Seems like it could be done without ISA.
With Ethernet and serial one can have access to most anything.

(OK, many people don't have a net (ethernet or slip) to connect to,
 but even then the Ethernet connector may serve as an expansion interface.
 There are a lot of devices (terminal servers comes to mind) that can be
 connected using Ethernet & tcp/ip))

} How hard would it be to put a floppy controller and parallel port on
} the mainboard compared to putting in a full ISA bus?
[...]

Floppy is useful.
Is a parallel port really necessary?  Serial printers should do, no?

BTW, what about second level cache?  Will it be difficult to add support
for it?  Just came to think about how badly many 486 boards perform when
running without cache enabled, or when one try to put more than 16 MB into
some of the boards with only 64 KB external cache.  (Oops, I hope I don't
initiate another cache flame war :-)

Regards,
Tor	([email-masked])

---

From: [email-masked] (Jeremy Fitzhardinge)
Date: Mon, 28 Jun 1993 12:48:53 +1000 (EST)

> since when one could only get serial versions.  Are ISA versions more useful?

Having ISA slots makes the board much more appealing to those with an
existing investment in ISA cards.  This is important.  If someone asks
"can I plug my soundblaster in to it?", its better to say "sure, you need
to write a driver though" rather than, "nope, design a scsi version".
More importantly, things like multiport serial/parallel boards aren't
things you want to clutter up a motherboard with, but are dirt cheap to
get in ISA form.

> Is a parallel port really necessary?  Serial printers should do, no?

Parallel is important.  There is nothing more useful than being able to
flash LEDs when nothing else works (either cause something is very broken
or because you're in the early stages of writing monitor code).