TELECOM Digest OnLine - Sorted: Re: Very Early Modems

Re: Very Early Modems

Julian Thomas (jt@withheld_on_request)
Wed, 25 May 2005 19:02:25 -0400

<as usual pse obscure my email address - tnx>

In <>, on 05/25/05
was typed:

>> 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.

> This was the IBM "Card-to-card" transceiver. I don't know when they
> first came out, but the Army started implementing them in a nationwide
> network in September of 1956.

I saw one in operation between the GE Lynn Mass facility and somewhere
else in 1960 or 61, in the same room as the 704.


> I believe they used 4-wire leased lines, with data access arrangement
> boxes provided by Ma Bell. So the signals going into the big grey box
> next to the reader/punch were analogue. I don't recall what the
> transmission rate was, but they sent EBCDIC directly without any
> translation to a 5-channel code and no added headers.

No, it would NOT have been EBCDIC, which didn't emerge until System/360
around 1965. Try BCD or maybe some 2 out of 12 code.

Julian Thomas: ID=jt domain=jt-mj period net
In the beautiful Finger Lakes Wine Country of New York State!
Warpstock 2005: Hershey, Pa. October 6-9, 2005 -

There are very few personal problems that cannot be solved by a suitable
application of high explosives.

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