Wang LOCI-2 Technology

See the LOCI-2 Data section for a 1967 Service Manual and a complete set of schematics

Electronics

The LOCI-2 is an electronic tour-de-force, built entirely from discrete diode-transistor logic. The architecture is rather extravagent with electronics, demonstrating great faith in the reliability of early 1960s transistors and diodes.

Architecture, Memory & Speed

The basic architecture appears to derive from 1950s computers and is very different from all other first generation calculators. The LOCI-2 is a Harvard Architecture small computer with a fixed program store on punched cards and all of its working registers implemented in electronics. This approach to storage is extravagant with electronics, 40 2-transistor flip-flops being required for the storage of a single ten-digit register. Five register-sized arrays of nearly 100 transistors appear on the circuit boards, contributing over 500 transistors towards the LOCI’s total of over 1200 transistors. This is more than double the number of transistors in other first generation machines.

Programs are loaded by placing a punched card into a Wang “bed of nails” card reader. The reader holds one card with up to 80 steps and a second reader can be attached to allow 160 steps to be accessed. If halts are placed in prograns then cards can be changed during processing and in theory there is then no limit to the size of the program. The LOCI is a true Harvard architecture machine, where instructions are entirely separate from data and cannot be modified by the machine.

The LOCI-2 has a small core memory which is used only for the machine’s data storage registers, despite Dr Wang being a pioneer of core memory. The basic LOCI-2 had four 10-digit storage registers and this could optionally be extended to 16 registers. Other first generation machines held working and storage registers in core or delay-line memory, allowing great savings in electronics. The LOCI architecture with working registers in flip-flops was more computer-like. It was not until the 300 series that Wang calculators took advantage of the savings that could be made by using core memory for all storage.

The LOCI-2 has been described as a fast machine and this results from two features in particular:

• its fully-electronic architecture with no processing delays due to core memory read/write cycles or delay line memory latencies
• the logarithmic computation engine that allowed multiplication, division and exponentiation to be done at electronic speed rather than program execution speed.

Construction

The LOCI-2 is constructed in a very utilitiarian manner which set the style of Wang products to follow. It uses clicky industrial keyswitches that were retained with little change until the end of the 400 series, nearly 15 years later.

The LOCI’s simple box-like case was improved upon for the later machines, but perhaps not by so very much. Internally, construction is solid and of high quality.

The fibreglass circuit boards are large and well-made but show Wang’s aversion to gold-plating for connector fingers, a practice that predisposes to corrosion and faults.

The power supply is of the most basic design. The main logic supply is -10V with no regulation and a 30% margin allowed. The only power supply adjustment is to trim the +6V level with respect to -10V and this is done by an adjustable tap on a large power resistor. The LOCI even lacks a power switch, to turn on one closes the protective circuit breaker and to turn off one uses the manual trip lever on the same circuit breaker.