TELECOM Digest OnLine - Sorted: Computer "Logic" in 1922 Panel Switching

Computer "Logic" in 1922 Panel Switching

hancock4@bbs.cpcn.com
17 Aug 2006 10:50:15 -0700

In 1922 the Bell System implemented "panel" dial switching in New York
City. The system had to handle a high volume of calls and a wide
diversity of central offices throughout New York City. This would've
been impossible with Step-by-Step which was limited to a 10x10 point
rotary switch. Panel translated the decimal exchange to codes for
hundreds of trunks as needed. Panel used common control to do this.
That is, it stored the telephone number and translated it as needed
for switching needs.

The control functions of panel were similar to modern computer CPU
instructions and I/O bus commands. An ingenius sequence switch,
loaded with numerous cams, controlled the functions. Different parts
of the switchgear would be selected, the unit would wait for a ready
signal, send out a command, then wait for a response and act
accordingly. Everything was run by a pulse train generator exactly
the same as a CPU clock today.

Signals between devices were self checking to detect errors. All gear
had internal error detection as well as test functions.

Remember this was all 1922, long before diodes and solid state
devices, indeed, tube electronics were brand new and still being
developed. It was all done with electro-mechanical relays. All
equipment had to be extremely durable and precise to handle a high
load volume and last in service a long time.

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