[GreenKeys] Teletype near Toronto

[Jim Haynes]

On Fri, 29 Apr 2011, Bill Horne wrote:
>   5. An RS-232 interface only works with a computer, and the design
>      decisions were made decades before microprocessors were invented.

RS-232 was originally developed for connecting "business machines"
such as Teletypes or computers to modems, at the time AT&T decided to
start offering modems for attachment to customer-provided equipment.
Until then the rule had been no "foreign" attachments to the switched
network, but when businesses began wanting to connect computers and
non-Teletype-made terminals of various kinds to the network they saw
they could not offer what the customer wanted, and so made it possible
with modems.  Also they realized there was substantial money to be made
from customers sending non-voice information over the switched network.

>   6. Vacuum tubes required AC power, at a time when many buildings
>      still ran on DC.

I don't think this is particularly relevant.  Tubes can run on DC.
There were some TWX station installations where a single channel of
43A1 carrier was used as a modem at the terminal. (before Dial TWX
and before modems built for the purpose of installation on customer
premises were designed. 
>
> I'd bet there are other reasons I haven't thought of, but I _do_
> remember that the first "103" modem I ever bought, which was the kind
> that had rubber cups for a standard telephone handset, had a
> current-loop interface built in to the same connector as the RS-232
> cable used.

That's because the modem maker realized there was a market for connecting
a Model 33 Teletype to the modem without having to buy the RS-232 
converter box that Teletype supplied as an extra-cost option.