TELECOM Digest OnLine - Sorted: Re: Very Early Modems

Re: Very Early Modems

Brad Houser (
Tue, 17 May 2005 12:46:39 -0700

On 16 May 2005 13:14:42 -0700, wrote:

> 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.

Here is a picture of a 1958 AT&T modem (not sure if this is the first
commercial modem, the Bell 103. If so it was 300 baud):

Brad H

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