In this section I'll accumulate documentation for the LGP-21 (and LGP-30,
in the case of software, with which the '21 is partly compatible).
Factory documentation
The LGP 21 Electronic
Computer System: Maintenance and Training Manual (ESD-1030)
is (21 Sep 2004) mostly scanned and now available. It's a great
document, containing a complete algebraic description of the
machine's operation as well as detailed descriptions of the logic
family, schematics, adjustment procedures (no minor thing for the
rotating memory) and complete documentation on the peculiar
Friden Flexowriter, specific to the LGP computers.
LGP-30 Subroutine Manual, containing important definitions, the
bootstrap code and procedures, etc.
In a Tally drawer was a few immaculate LGP-21 Optimum Address
Calculator, a circular slide rule for determining the
most-optimum memory location. Here's the rear with order chart.
LGP computers used customized Friden Flexowriters
as "console" and boot device. They use this very peculiar
6-bit character code, in two
cases, with ITA2-like FIGS/LTRS case-control characters; the
character codes map directly (in hardware!) to machine
instruction opcodes. I swiped this chart from Dik Winter's
"http://www.cwi.nl/~dik/english/codes/7tape.html#lgp30" codes
website, without permission. Note Dik's comment about "l" vs.
"1"... there is a unique way to distinguish internally between
the two, but not visually on paper!
Ed Thelen's incredibly useful
"http://ed-thelen.org/comp-hist/lgp-30.html" LGP-30 website.
The LGP-21 is almost-code-compatible with the '30. See also his
="http://ed-thelen.org/comp-hist" antique computer
and Nike
missile sites.