[GreenKeys] FTGH - M28 LARP1 multi-magnet reperf

[Jim Haynes]

The main use of the LARP was in fully automatic store-and-forward message 
switching systems, such as Western Union's Plan 55 used by the Air Force 
in the late 1950s - early 1960s.  In one form of such systems messages are 
received on reperforator tape.  Each reperforator tape feeds directly into 
an associated tape transmitter.  There the message directing codes are
read and interpreted, and then the tape transmitter is connected to a
"cross office" reperforator associated with the outgoing line.  The
message is sent across the office and perforated a second time, where
it then feeds a tape transmitter that transmits to the selected
destination.  If the cross-office circuit is busy when a message comes
in then the message has to wait at the incoming-side tape reader until
the circuit is free.

It is a principle of these systems that you want the cross-office
transmission to be faster than the incoming lines.  This way you hope
to find the cross-office circuit non-busy when it is needed.  So the
incoming side tape reader and the cross-office reperforator may be
operated at 200 wpm for that reason.  The W.U. Plan 55 system used
electronic transmitting and receiving distributors to achieve 200 wpm
cross-office transmission; and then the character punched was compared
with the character read to detect any failure in the reperforator or
its driver circuits.  Older W.U. systems transmitted characters cross-
office in parallel to achieve higher speed than the transmitting and
receiving distributors of the day could handle.  Which meant that the
cross-office circuit had to switch about nine wires for the bits of
the character plus various control signals.

There was some minor use of the LARP for other applications where a
high speed punch was wanted but not badly enough to justify the
1050 wpm BRPE.  Or applications where the information was already
in parallel form so it would have been extra trouble to convert it
to serial for a conventional reperforator.