TELECOM Digest OnLine - Sorted: Very Early Modems


Very Early Modems


hancock4@bbs.cpcn.com
16 May 2005 13:14:42 -0700

In the IBM history series by Pugh et al, they said IBM converted
punched cards to paper tape for transmission in the 1940s. My guess
is that that particular transmission used telegraph TTY lines (not
voice) of either AT&T or Western Union. Recall that AT&T maintained
telegraph long distance lines as part of carrier long distance
circuits. Because of the low bandwidth, a telegraph channel could be
carried on the low end of a carrier channel. Accordingly, no
modulation was required and thus no modem needed.

It was also said IBM limited development in this area to avoid
annoying AT&T who was IBM's best customer.

However, in the 1950s, IBM developed card-to-card directly without
paper tape and "over AT&T lines". Modems were developed to take good
advtg of the available bandwidth (about 1200 baud). Undoubtedly the
equipment and implementation was developed in close cooperation with
AT&T.

I was wondering if the modems in that application were supplied by IBM
(who appears to have developed the technology) or by AT&T. My
understanding that AT&T's "Dataset" modem-telephones didn't come out
until the 1960s.

Comments by anyone familiar with pre-1960 data communications would be
greatly appreciated.

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