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).
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 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
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