Was it 110, 135, then 300?

From: Derek Peschel <dpeschel_at_eskimo.com>
Date: Fri Oct 27 04:44:17 2000

> What was the progression in modems? Was it 110, 135, then 300, or were the
> first two speeds pre modem technology?

I'm not sure if there was _a_ progression, but anyway...

No, the first two speeds were not pre-modem technology. The early Teletypes
(with the five-bit character codes) work at around 45 bps (or more if you
change the gears). The later models with ASCII work at 110 bps. Many units
have direct connections through current loops, but some have modems.

BTW, the technique they use is still used today and called by the same name:
Frequency Shift Keying. "Frequency shift" is because the two bits are
represented by tones of slightly different frequencies, "keying" because the
Teletype was regarded as a distant descendant of Morse's telegraph key.
There is an intermediate machine, named after its inventor Wheatstone, which
uses a typewriter keyboard, punched paper tape, and electric transmission of
the signal, but works directly in Morse Code! The printer that goes with
this setup prints dots and dashes on a narrow strip of paper.)

The 135-bps speed was created by IBM for their typewriter terminals.

Another type of machine -- which uses a modem but for an analog signal --
is a certain type of fax machine. It's not necessarily relevant but it's
interesting (and fun to watch).

-- Derek
Received on Fri Oct 27 2000 - 04:44:17 BST