LGP-21 Documentation

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.
• LGP-21 Sales Brochure (G3-3101)
• Brochure of Civil Engineering Software for the LGP-21
• The LGP-21 Programmers Manual; from "http://ed-thelen.org/comp-hist/lgp-21-prog-man.html" Ed Thelen's site and a copy of it here.
• Tangentially related, the RPC-4000 Reference Manual, a more recent Royal McBee product.

Other documentation

• This operating procedure sheet came with this machine.
• Here are some photographs of the machine, reasonably unorganized for now.
• The memory and number representation scheme of the LGP-21 and LGP-30 will seem rather bizarre if you've only worked with "modern" machines.
• LGP punched tape digit representations was in a drawer in one of the Tally devices.
• Here's a price sheet originally published in Weik's "A Third Survey of Domestic Electronic Digital Computing Systems" Report No. 1115, March 1961.
• This example of LGP punched tape digit representations was in a drawer in one of the Tally devices.
• 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.