What's the difference between a 1542A and a 1542B?

[Jay Ts]

In article <1990Dec21.113850.4872 at nstar.rn.com>, larry at nstar.rn.com (Larry Snyder) writes:
> kevinr at sequent.UUCP (Kevin W. Rudd) writes:
> 
> >	Can anyone tell me what the difference is between Adaptec's 1542A and
> >1542B SCSI controllers is?  I am planning on using one of them in an ACMA
> >386/20 system with a Maxtor SCSI drive.  I have heard of problems with the bus
> >mastering on these boards.  Does this apply for both the A and B?  Is there a
> >way of telling whether the system will have trouble with the board before
> >forking out the money for one?  Any advanced advice would be helpful.
> 
> I remember seeing your original posting, the 1542A is physically a larger
> board (full sized) while the B is a 2/3 sized board.  Throughput is the
> same on board boards.

(Just my opinion, but the 1542B seems much better constructed, too.
A nice product, if you ignore the almost nonexistent tech support by phone;
the recorded message I got said, effectively, "leave us alone and go talk to
your reseller".  They must have learned to do this from ISC :-)

Due to a failed floppy controller, I just had to replace the 1542A in my
system with a new 1542B.  I was a bit nervous, too, from reading of the
above-mentioned problems, so I called ISC and ESIX, and they did not
have any reported problems on file.  In any case, I *had* to replace
the failed board real quick to get my system running again.

I tried the 1542B, and found that it works with ISC 2.0.2 and ESIX rD with no
problem (on *my* system).  I'm not sure, but I think one or two defaults may
be different.  For example, (I should really go check this, sorry...) I think
the default DMA speed for the 1542A was 5.0 Mb/sec, whereas the jumper on the
1542B is shipped as 5.7 Mb/sec.

Well, I guess I've left a hole for Roy Neese at adaptec to fill in if I'm
wrong.  Um, Roy?

And if anyone needs a 1542A with a nonfunctional floppy controller (the
hard disk controller still works), give me a buzz ...

> The 1542 with a pair of fast SCSI drivers will out-shine most other
> disk configurations (at least with 386/ix).  I am happy as can be with
> the SCSI disk subsystem here on nstar --

.. Otherwise, I'll just save it for a future upgrade!

				Jay Ts, Director
				Metran Technology
				uunet!pdn!tscs!metran!jay