[GreenKeys] A Little More TWX History

[Harold Hallikainen]

While looking for something else, I, of course, ran across this, which I
thought would be interesting to the group.

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Date: Tue, 2 Mar 1993 14:26:39 -0800
From: haynes at cats.UCSC.EDU (Jim Haynes)
Subject: A Little More TWX History

Well of course the original TWX goes back to about 1930, used 3-row
machines, and manual switchboards.  In fact the introduction of TWX
was what caused AT&T to buy the Morkrum-Kleinschmidt Corp. and rename
it Teletype.  At the time the service was provided using
telegraph-grade circuits.  You'll occasionally see a picture of an old
TWX switchboard, maybe in an old encyclopedia.  The switchboard
operators used tape-strip printers to communicate with the customers.
Telex was in use in Europe in about the same time frame, and used SXS
switching technology and telegraph-grade circuits.

Western Union introduced Telex to the U.S. in the early 60s.  This was
probably a bad mistake for them.

   1) They had to buy a lot of electromechanical switching equipment
      which was soon to be obsoleted by electronic switching.

   2) AT&T was about to move TWX to the voice switched network, where the
      enormous volume of voice service had driven the cost of connections
      and bandwidth way down.  The telegraph-grade lines were no longer
      cheaper than voice circuits; they were in fact more costly to AT&T.

   3) It put W.U. into practically head-to-head competition with an AT&T
      service; and AT&T was a much stronger company financially.

   4) W.U. was usually dependent on the telephone companies for local loops
      between customers' offices and the nearest W.U. office.  Thus W.U.
      was at the mercy of its competitors rates for these private lines.

As an aside, European Baudot machines tended to have four-row
keyboards.  The digits were on the fourth row, like a typewriter.
There were blocking bars such that if the machine was in FIGS case the
digit keys were unblocked and the corresponding letters keys were
blocked.  So the user still had to send FIGS and LTRS as in the U.S.;
it was just that the European machine design took a slightly different
direction from that in the U.S.

The European machines also tended to have built-in paper tape
facilities of the limited sort that Teletype introduced into the Model
32 and 33 machines.  In previous Teletype designs the paper tape
equipment was mechanically independent of the keyboard and printer.
You could, for instance, be punching a tape from the keyboard at the
same time you were receiving a message on the printer; and you could
be sending from tape at the same time you were punching another tape
from the keyboard.  In the European machines, and later in the
Teletype 32 and 33, the tape punch had some parts in common with the
printer and the tape reader shared some parts with the keyboard.
Hence you couldn't use the keyboard while sending from tape; you
couldn't punch a tape from the keyboard while printing something else,
etc.

The Teletype Model 15 has been mentioned as a heavy-duty machine
dating from 1930.  In the late 1930s some of the Bell companies asked
for a less expensive machine for TWX service, recognizing that a lot
of offices could use TWX but didn't need the heavy-duty machine.  (The
Model 15 is what was used for AP and UP news wires through the 1950s.
It could stand up to the around-the-clock printing that occurs in that
service.)  The answer to this request was the Model 26.  The 26 used a
rotating type cylinder holding individual slugs of type.  The cylinder
stayed in one place and the paper platen moved from side to side as in
a typewriter.  (In the Model 15 and the later machines the paper
platen is stationary and the printing element moves across the page.)

The Bell System phased out the Model 26 machines in, oh, the late 40s
and 50s.  The machine didn't save enough in first cost to be worth
supporting both it and the Model 15 in terms of parts and maintenance
training.  Lots of Model 26 machines wound up in amateur radio
service.  The hams formed organizations to plead with the Bell
companies to sell their used machines to hams rather than breaking
them up (to prevent their falling into the hands of those who would
use them in competition with Bell services).  Hams had to sign a legal
form to the effect that they would not use the machine outside the
hobby, and would not sell it to anyone without requiring a similar
promise.

In the late 50s and early 60s came all the work that resulted in ASCII
 -- first the upper-case-only 1961 ASCII and then the up/low 1968
ASCII.  Prior to ASCII there were lots of codes floating around.
Teletype made the Model 29, which was an eight-level four-row machine
working on one of the IBM BCD codes.  I believe this was used only
internally in Western Electric; AT&T was scared to put an IBM coded
machine out to the public lest non-IBM computer makers complain that
the AT&T giant was favoring the IBM giant at their expense.  The Model
35 was based on the 29; in fact I'm aware of some people converting 29
printers to ASCII by changing just a few parts.  Many parts were
common between the five-level Model 28 and the eight-level Model 35.

The Model 32 and 33 machines actually started as a project to develop
a light-weight machine for the military.  The light-weight project
didn't get very far; but a lot of the ideas wound up being used in the
low-cost printer project.  Again the Bell companies and Western Union
saw a need for a machine that would cost a lot less than the
heavy-duty machines, for use in offices that didn't have a lot of
traffic.  I might mention that Western Union dabbled in making its own
teleprinters from time to time; occasionally one will see a sample of
their Model 100 family.  I believe W.U. was the main customer for the
32, for Telex service and the Bell companies were seen to be the main
customers for the 33 for the new four-row dial TWX service.  These
machines had most of the parts in common.  They were available with
and without paper tape; where paper tape was present it followed the
European style, so you couldn't do all the things with these machines
that you could with a 28 or 35.

The design objective for the 32 and 33 was that they would be used on
an average two hours per day.  Cost was held down by not heat treating
and hardening and nickel plating the parts; some adjustments were made
by bending parts rather than by moving parts on elongated holes and
that sort of thing; assembly was designed for high volume with a die
cast base and self-tapping screws and parts that snapped together
without bolting.  Meanwhile along came the minicomputer companies who
adopted the 33 as a console device, where it often ran around the
clock (and generated a lot of cursing about the frequent need for
maintenance).

For manual TWX Teletype supplied a basic machine to the phone company,
which added some kind of Western Electric box on the wall for line
interface.  This might be a carrier channel terminal or some relays
for a D.C. line; and there were schemes where ringing was used to
control the motor on the Teletype machine, and schemes for cutting off
current in the line when it was not in use.  Telex and dial TWX
required additional components for setting up and controlling the
call.  The Model 32 for Telex had a built-in Call Control Unit with a
dial and line relays, all ready to connect to the D.C. local loop.
For dial TWX there was a Western Electric modem stashed in the
Teletype stand and a variety of call control units (pulse dial, tone
dial, card dialer, loudspeaker vs. earphone, etc.)  made by Teletype
and connecting to the modem.  This was a source of considerable
annoyance to Teletype, as the interface involved 99 wires, each of
which was negotiated between the modem designers at Bell Labs and the
call control unit designers at Teletype.  A little later some of the
Bell companies would save money by furnishing a Bell modem with
built-in telephone connecting over a few-wire cable to a Teletype
private-line-version machine having no call control unit.

There is a lot of weird and interesting (perhaps) lore connected with
the modems.  Since dial TWX used a voice-bandwidth connection they
could afford the luxury of full duplex modems using two different
frequency pairs for the two directions of transmission.  This
introduced the complexity that a modem had to know whether it was
originating or answering a call to know which pair of frequencies to
use for which purpose.  Even after Bell began supplying modems for
connection of customer-provided data equpment (just before Carterfone)
these modems could function in either originating or answering roles.
After Carterfone the suppliers of modems for computer time sharing
could take advantage of the fact that the terminal always originated
and the computer always answered; so we got reduced cost
originate-only and answer-only modems.

It always seemed to me that the TWX section of Bell Labs was
controlled by old geezers who had been around since 1930 and couldn't
imagine that a TWX machine would ever want to talk to anything except
another TWX machine.  If you wanted to use the same kind of Teletype
machine to talk to a computer, well that was another matter entirely.
The modems had separate originate and answer frequency pairs, each
binary FSK.  This permitted two options for which frequency pair would
be originate and which would be answer, and four possiblities (two for
each pair) of which frequency would be mark and which would be space.
Thus it was possible by wiring options to set modems up for as many as
eight mutually-incompatible services, all using the same voice
switched network without any restrictions on area codes and numbers.
I remember hearing about TWX, and TWX-prime, and WADS (wide area data
service) and WADS-prime, all of which were to use the same modems and
switched network without any of these being able to communicate
outside its own service.  I guess they had in mind different tariffs
for TWX machines talking to TWX machines versus terminals talking to
computers, versus some other things.  Practically all of this was
swept away by Carterfone.


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