ISA expansion boards/cases

From: Eric Smith <eric_at_brouhaha.com>
Date: Sun Oct 10 00:34:54 1999

Adam asks:
> Is there a good place to find boards that plug into a 16bit ISA slot and
> let you have another 8 or so slots? (without building your own)

I wouldn't bother. They don't work reliably. There are two
types:

1) Unbuffered. These don't work because well-designed ISA cards barely
    have enough drive for 8 slots, and cheap crap (including some common
    brand-name stuff) only has enough drive for 2-3 slots. Even with the
    well-design stuff, once you figure in the added capcitance of a cable
    and another backplane, it won't work reliably even if you're just trying
    to expand a modern motherboard with only 1-3 ISA slots.

2) Buffered. These have all sorts of limitations regarding bus mastering
    cards. Even if you don't need bus mastering, they introduce enough
    delay into some of the critical ISA signals that many cards won't work
    properly. The signals that a card has to assert to indicate to the
    motherboard whether it is 8 or 16 bit, and whether it needs wait states,
    are very time critical.

It's been over five years since I looked into these, and I doubt that there
are any better solutions now than there were back then. If there were any
good solutions, I guarantee that they would cost a lot more than $500. The
fundamental problem is that ISA is a crappy excuse for a bus. It's very
poorly designed; IBM just brought out the processor signals to the connector
in the PC and XT, and kludged more crap on for the AT.

On the other hand, PCI is actually a pretty well-designed bus, and it is
quite possible to build an expansion box for it. Bit 3 (apparently now
a subsidiary of SBS) makes some nice boxes. But I think they sell for
around $1000.

What exactly do you need to interface to the ISA bus?
Received on Sun Oct 10 1999 - 00:34:54 BST