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From: mju@ganglion.ann-arbor.mi.us (Marc Unangst)
Newsgroups: comp.unix.sysv386
Subject: Re: Suggestions for 386SX/SVR4 platform
Message-ID: <1991Jun4.011149.9227@ganglion.ann-arbor.mi.us>
Date: 4 Jun 91 01:11:49 GMT
References: <8808@fed.FRB.GOV> <2100@ecicrl.ocunix.on.ca>
Reply-To: mju@mudos.ann-arbor.mi.us
Distribution: usa
Organization: D.J. Services
Lines: 33

In article <2100@ecicrl.ocunix.on.ca> clewis@ferret.ocunix.on.ca (Chris Lewis) writes:
>>One other thing: does anyone know if internal Telebit 
>>modems are commonly supported by SVR4 implementations?

One thing to watch out for is that the Telebit internal modem has a
non-16550 UART in it, which means that the CPU is interrupted on every
character.  If you're downloading news at 1300cps or so, that means that
the CPU winds up servicing a serial input interrupt about every 3/4ms or
so.  This can really put a strain on the CPU, and can also lose characters
on input.  If you have a serial port with a 16550 UART and a serial driver
(such as FAS) that supports it, you only need to interrupt the CPU every
16 bytes or so, which is much easier on the CPU.

The UART on the TB modem also isn't socketed, which means in order to
replace it, you have to unsolder it -- which, naturally, voids your
warranty.

Finally, internal modems are a bad idea in any case.  They can't be moved
from one bus architecture to another, which means your modem won't work
on a Sun workstation, DECstation, or anything else that doesn't have an
ISA bus.  Internal modems also can't be turned off without turning off
the whole system, and you don't want to have to shut down your Unix system
just because your modem got confused.  Finally, internal modems tend to be
very good at shunting lightning spikes that come across the phone line
onto your bus, which means if your phone line gets hit, you could well
fry your motherboard and some of your other expansion cards.  If an
external modem takes a lightning hit, it usually dies, but at least it
doesn't take the rest of your system with it.

-- 
Marc Unangst               |
mju@mudos.ann-arbor.mi.us  | "Bus error: passengers dumped"
...!hela!mudos!mju         |