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IME 86S Technology


Electronics

IME 86S
First-generation fully transistorised machine. Germanium PNP transistors.

Architecture, Memory & Speed

  • 16 displayed digits plus sign indicator.
  • Digits encoded as 4-bit BCD,
  • Core memory,
  • @@kHz master clock, @@mS core cycle, @@mS full-number time

Construction

The stylish 2-piece diecast case separates and can be removed to reveal a fully self-contained electromechanical chassis that is very clean and tidy. The bare chassis is almost able to stand as a finished unit, in contrast to most other first generation machines which reveal a maze of wires, components and brackets when uncovered.

The electronics are contained on 34 single-sided phenolic PCBs. Spreading the electronics over many relatively small PCBs permits the stylish low profile cabinet but at the cost of many more edge connector contacts, which can be a source of trouble. At least IME gold-plated the PCB contacts, unlike Wang who employed a similar scheme of many small PCBs but without gold plating. Trap for the unwary: in this model the core memory occupies slot 24 and is hard-wired. Do not attempt to simply pull this board out!

The IME’s design elegance is further revealed after removing four screws from one side of the electronics package, which then splits on a hinge at the rear and exposes the wired backplane that was hidden within. The backplane is then easily accesible for signal probing. No other dawn-age calculator has been seen with this level of design applied to its internal construction.

The keyboard is slightly surprising, being a leaf switch design with two contacts in parallel for each switch. Leaf switches are electrically noisy and are less reliable than the magnetic reeds or spring microswitches that were used in most other first generation machines and one wonders why this choice was made.

The logic boards use Raytheon T6056A transistors almost exclusively. No information has been found about this particular transistor but an interesting question is raised by its use. Raytheon was one of the earliest US manufacturers of transistors but by the start of the 1960s Raytheon’s semiconductor operations were struggling. In 1962 Raytheon decided to leave the semiconductor business and within two years or so Raytheon’s semiconductor business had ended. The IME 86 dates from after 1964 and this raises the question of how IME had such a large stock of Raytheon branded transistors in the mid and late 1960s. Perhaps the T6056A was a custom production item, this may explain the lack of data and IME being able to obtain large quantities even as the Raytheon transistor business was ending.