External links

Documents in English

Reference Manual – a great introduction to the instruction set and user interface, plus reference information on character set, representation of numbers, and optimum placement of data and instructions on the disk.
Programming Manual – more details on the instruction set, an introduction to programming, details on number and character representation and tape preparation. Some overlap with the Reference Manual.
Maintenance and Training Manual including schematics and derivation of the logic equations. Also includes documentation and alignment instructions for the Flexowriter and magnetic disk.
The 1964 BRL report gives specs and detailed pricing for the LGP-21.
A flyer describing the Librascope LGP-21 with full specs, a summary of the instruction set, and good information on the target market and applications.

Documents in German

The University of Stuttgart’s online archive also offers quite a bit of documentation on the LGP-21, mostly the Schoppe & Faeser version. Among other documents, this includes schematics, functional descriptions and installation instructions for several upgrade options for the LGP-21, which I find quite fascinating. A few notable documents:

Service manual with schematics.
User instructions giving step-by-step instructions on booting, loading and compiling programs. A “bare bones” typescript; see the English user manual for an illustrated user guide which also describes the control panel.
Fast memory upgrade, early version: Two additional pairs of read/write heads could be installed on a spare disk track, and would provide one 32-bit and one 64-bit memory cell which auto-repeated during every word cycle (just like the accumulator and other CPU registers). Functional description with logic equations and block diagram. This was a complex upgrade comprising seven extra circuit boards. The schematics for the individual boards are also available on the Stuttgart server; look for the drawing numbers listed on page 1 of the functional description.
Fast memory upgrade, later version: Using electronic shift registers instead of disk tracks, this version provided four 32-bit words of random access storage, one of which could also be used as an index register when addressing the main memory. User description, schematics and technical description with modified logic equations and installation instructions.
Double-sized memory was available as another option. The memory disk was replaced by a disk with a second set of 32 main memory read/write heads on its bottom side. Some minor changes to the P (track address) flip-flop logic were made by manual wiring changes – described in the installation instructions. The instructions refer to these schematics of the command control and I/O board.
Sequence Tag Mode was a high-speed mode of operation, which could be enabled and disabled under software control once this upgrade was installed. It enabled the execution of up to 32 instructions per disk revolution, vs. a maximum of 7 instructions per revolution in a fully optimized program in regular mode. User documentation and technical description with schematics and logic equations. — Sequence Tag Mode may have been “borrowed” from the Packard Bell PB 250, a competing serial memory computer based on acoustic delay lines, introduced in 1961. See page 8 of the PB 250 reference manual. Stan Frankel, the designer of the LGP-30, is said to also have been a consultant on the PB 250 design.
Priority control added an interrupt capability to the LGP-21, for use in process control applications. Eight external interrupt lines were added, each of them triggering a subroutine call to a predefined address. Only the user documentation is available for this upgrade; I am not aware of technical documents for the required additional board. (Which must have been a complex one, taking up two slots in the LGP-21 according to the user documentation.)

Librazette journal

A group of former Librascope employees maintains the Librascope Memories website. Among other documents, this site hosts a complete collection of the Librazette – an employee newsletter published from 1940 to 1999.

The Librazette gives a good impression of the development of Librascope as a division of General Precision, and later Singer, over several decades. It clearly shows the strong focus Librascope had on military technology, but the “commercial computer” product line gets its share of attention as well. A few issues relevant to the LGP-21:

March 1963, page 2: The LGP-21 is launched at the IEEE show in New York.
May 1963, page 4: An update on orders and pricing for the LGP-21. Also a full-page ad on page 8.
November 1963, page 10: Blackjack remains a staple for showing off the LGP computers. This article seems to describe a custom program which let the LGP-21 act as a player, beating the house during a Las Vegas computer show demo.
May 1964, page 10: A full-page ad focusing on the LGP-21’s applications in Civil Engineering.

And a few issues mentioning key organizational changes:

April 1962, page 2: General Precision acquires Royal McBee’s share of the “Royal Precision” joint venture in commercial computing, making it a wholly-owned General Precision business. Also, a European representative for Librascope is appointed, pictured on page 3 together with Kurt Bojak, the president of Eurocomp.
May 1962, page 1: The new “Commercial Computing Division” is formally established.
June 1964, page 9: An update on General Precision’s presence in the European market.
August 1965, page 3: The “Commercial Computing” business is sold to Control Data Corporation. Librascope/General Precision will only produce components for 3rd party computers going forward.

More to come…

The technikum29 has a large collection of paper tapes, comprising the ACT compiler for the LGP-21 and a largely complete library of subroutines. The collection also comprises original manuals for the software library and compiler. To my knowledge, this software is not available elsewhere. We plan to make it accessible on the technikum29 website soon!