Wang LOCI-2AC Calculator
Logarithmic Calculating Instrument

The Wang LOCI-2 Programmable Calculator was introduced in January 1965, replacing the LOCI-1 that was introduced just four months before. The LOCI-2 has more than 1,000 transistors, no integrated circuits, core memory, and National NL-8421/5092 Nixie Tubes for the display. To dramatically improve the speed of multiplying and dividing it actually added or subtracted logarithms. It supported a printer, Teletype, and punched card reader peripherals.

Our LOCI-2 was shipped as a model 2AC, so it has 16 Storage Registers in core memory and a 1412A Teletype interface. It doesn't have a 1407 Storage Register board because it is a model 2A and has a 1410A 16 Storage Register board instead.

Our LOCI-2. #3026, came from the Wang Connecticut Customer Engineering office. It was used in the late 60’s and early 70’s as a test bed and repair kit for field service engineers. If they couldn’t repair a board in the field the defective board was sent to the Wang home office and exchanged for a functioning one. We also received a salesman's case containing a complete set of spare boards, a card reader, and a complete keyboard.

Numbers are stored in the registers in Binary Coded Decimal format. There is a 1, 2, 4, and an 8 bit for each digit in a number. The decimal value of a digit is the sum of the bits for each weight, e.g. a 9 is stored as a 1 and an 8. Each bit is stored in a flip-flop made from two transistors. Most registers are 10 digits wide, so it takes 2 x 4 x 10 = 80 transistors to make a register.

The boards in this LOCI-2 calculator are:

  1. 1501 Input Decoder Control for the Card Reader and Teletype

  2. 1401A Register Decoder and NIXI Display

  3. 1402A W-Register with Binary Adder

  4. 1403B L-Register with Binary Adder

  5. 1404A Main Timing

  6. 1405A Miscellaneous Shift Pulse and Control

  7. 1406A A-Register with Accumulator, Decimal Counter

  8. 1408A Program and Decrement Counters plus Storage

  9. 1412A Teletype Input and Output Control

  10. 1410A 16 S-Registers Containing 10 Digit Decimal + Sign of Each Register (Core)

The restoration blog is here.

There are a few LOCI-2 calculators left, most in private collections. These are the public ones:

The point-to-point wiring on the bottom of the chassis. The circuit breaker at the bottom right is broken and will need to be replaced. It looks like the capacitor for the +10VDC power supply is installed backwards. It looks cleaner than the one at the left for the NIXI power, so it was probably replaced at some time.

This LOCI-2 belonged to Wang field service and came with a case full of spare boards. The field service people would install known-good boards from the case to repair a customer's calculator. Then they would install the broken board in this LOCI-2 to determine the fault, repair the board, and put the repaired board back in the case. This LOCI-2 came with two punched card reader to load programs. Since this LOCI-2 is a Model 2AC it supports a Teletype as an I/O device using the 1412A board that goes in slot 9.