IME 86/IME 86-S Electronic Calculator

The Old Calculator Web Museum is pleased to have acquired an IME (Industria Macchine Elettroniche, S.p.A.) IME 86-S calculator and associated peripherals for exposition in the museum. Sincere thanks to Serge Devidts for picking up the machine in Germany and arranging for shipment to the museum.

The IME calculators were the brainchild of Italian engineer and inventor, Massimo Rinaldi. Rinaldi was an expert electronics designer, skilled in transistorized digital electronic design, through education in Italy and later work in the field. In the early 1960's, Rinaldi became aware of a desktop electronic calculator built in England called the Anita. This machine used electronic tubes called Thyratrons and Dekatrons to perform math at a much higher speed than motorized mechanical calculators, and it did so silently. Rinaldi believed that he could design a better electronic calculator based on transistorized computer technology what would make for a smaller, faster, and more reliable desktop calculator. He developed his own prototype machine that was used to convince investors that his machine was a major improvement over the British machine. In 1963, Industria Macchine Elettroniche, S.p.A. was formed as a subsidiary of the large Italian diversified conglomerate, Edison Group. A shop in Rome, Italy was set up, and work began immediately on turning Rinaldi's prototype into a production quality desktop electronic calculator.

The resulting machine, the IME-84, is stated by IME as being the first solid-state electronic calculator. While the IME-84 was among the earliest transistorized electronic calculators, there are other contenders for the title of first solid-state desktop electronic calculator to market. Along with the IME 84, there were the Friden 130; the Monroe EPIC-2000; the Mathatronics Mathatron, and the Sharp Compet 10. All of these machines came to mass market during 1964. Who was actually first is a battle of definition more than anything else, as some of the machines were introduced in 1963, but weren't actually available for customer shipment until sometime in 1964. There are also some issues about the true definition of solid state. Some of the machines (the Friden 130 and Monroe EPIC 2000, for example) utilized magnetostrictive delay lines as their data storage medium -- a technology which can be argued is more electromechanical than solid-state. The Mathatronics Mathatron was truly a solid-state machine, using magnetic core memory for storage. The Mathatron was shipped to its first paying customer in late 1963, so technically, it predated the IME 84 to market.

The early IME calculators were masterpieces of design; electronically, mechanically, and aesthetically. Electronically, the machines used computer engineering concepts in the logic design, making the machines similar in architecture to small computers. Some of the other early calculators used architectures similar to their mechanical predecessors, with circuitry that counted by tens instead of using binary arithmetic; and utilized control methods that were essentially electronic emulations of the cams, gears, and linkages that made mechanical calculators operate. The logic of IME's machines was designed to be extensible, providing the potential for addition of peripheral devices. Mechanically, the machines were packaged such that they were modular, making for ease of service. Despite the modular design, great efficiency in space utilization was part of the design, to make the machines significantly smaller than that of competitors, while still providing sufficient cooling through convection to avoid the need for a noisy fan. Stylistically, the machines were sleek, with a very modern look that made them the technology centerpiece in any setting. From an operational standpoint, the early IME calculators could be a bit daunting to use for someone who was not familiar with their operation. The machines use a three-register architecture, with an input register, an accumulator register, and a counter register, similar to the three register architecture of later design electromechanical calculators. The user had to select the proper register for inputting numbers into the machine, and also to display the correct register containing the result of calculations. Other calculators from the period were easier to use, with a stack architecture (Friden, Monroe), pure algebraic logic (Mathatronics), or a simple arithmetic architecture (Hayakawa/Sharp).

The IME-86 was a follow-on to the design of the IME-84, designed to provide even more expandability than its predecessor, as well as making improvements to make the machine easier to use. It is based on the same basic design concept as the IME 84, but with greater numeric capacity, and the addition of an (optional) single-key square root function. There was also the IME 86-S model, which added the capability to interface to a diverse range of peripherals. With its peripheral capabilities, the IME 86-S could become the centerpiece of a true computing system that could rival small computer systems of the time, at a much less expensive price tag.

An IME KB-6 Remote Keyboard/Display Unit

The IME-86-S calculator was designed to be the centerpiece of a multi-component calculating system. The machine was designed with expansion capabilities in mind. A fairly wide range of options were available for the machine, including remote keyboard/display units (Model KB-6) which could connect to the main calculator through a "hub" that allows up to sixteen remote keyboard/display units to be connected, although only one unit at a time can access the calculator (unlike the Wang 300-series "SE"-model calculators, which could serve four simultaneous users). Also available were an external printer; keyboard-only units; external core memory expansion units (MS-30/MS-60) and programmer units, including the Model DG-308 and DG-408 "Digicorder" devices that transform the IME 86 into a learn-mode programmable calculator. The Digicorder programmers also provide a built-in punched card reader that allow read-in of programs from specially coded 8-channel edge-punched cards. Along with the desktop calculator form-factor, IME also produced rack-mount versions of the calculating engine (IME 86-S RM) and peripherals that would allow a complete calculating "mainframe" system to be created.

The IME Model DG-308 Digicorder
Image Courtesy Serge Devidts

The IME 86 is a discrete transistor (mostly Germanium PNP 2N1305 transistors) calculator, with sixteen digits of beautiful Nixie tube display. Magnetic core memory provides working register storage.

The IME 86S (as well as all of IME's first generation calculators) were exquisitely designed and built calculators. The electronics of the IME 86-S are packaged in a beautiful "split" card cage that is designed to split down the middle with a hinge allowing access to the amazingly beautifully-done hand-wired and bundled backplane. The circuit boards slide into the card-cage from the left and right-hand sides of the machine. All of the circuit boards other than the magnetic core memory board are standardized with 22-pin single-sided edge connectors that provide connectivity to the backplane. The edge connector fingers are gold-plated for reliability. The edge connectors sockets feature "death grip" contacts that very securely grab the circuit board, holding it in place. The card cage is made from plastic castings that screw into a sheet metal frame. The plastic castings have cast-in guides for the circuit boards. A metal clip snaps across the opening for the circuit boards on each side of the card cage to assure that the upper and lower parts of the card cage securely grip the circuit boards. The circuit boards are made of high-quality phenolic material, are are a bit thicker than used in many other calculators, providing a rigid base for the components. Circuit traces are etched on the back side of the circuit board, with through-hole mounted components. Wire jumpers are used on the component side of the circuit boards to provide connections where the single-sided trace routing can not accommodate the connections. The of the logic of the calculator is contained on 38 circuit boards, 37 of which are removable, with the core memory board being hard-wired into the backplane.

The calculator carries out the basic four math functions along with an optional automatic square root (which uses memory register IV as a scratch register during the calculation, causing it to be cleared). The square root function logic is built into the machine's logic, with the cost of the square root option simply being that of providing a different keyboard bezel with the hole for the square root key, and the key-switch assembly for the function soldered into the circuit board, which already has pads for the switch in place. It also appears that there was a version of the IME 86-S with two memory registers (I and II) instead of four (I, II, III, and IV). There is some confusion about this, though, as it appears that the original IME 86 (without the -S) did not have square root as an option, and came by default with two memory registers, but could be had optionally with four. The confusion comes with the fact that square root is an option on the 86-S, so the question ends up being, what is the difference between an IME 86 (which doesn't have square root), and an IME 86-S without the optional square root function? At this point, supposition is all that can be made with regard to this, with that being that the IME 86 was originally designed without the logic for calculating square root. Some time after the IME 86 was introduced, it seems possible that either marketing deemed square root as a desirable function to be added to the machine and engineering went about the task of reworking the logic to include the function, or, engineering saw that adding square root was a feature that could relatively easily added to the existing architecture without too much fuss and went ahead and implemented it, providing an optional additional valuable feature, especially for engineering and scientific calculations. Four accumulator-style memory registers are provided, making the machine particularly useful for more complex operations involving multiple intermediate results. The memory registers can also be configured as constant storage registers for holding constants used in more complex calculations. With a capacity of sixteen digits, the machine provides plenty of capacity for financial or scientific calculating. The 86 is a fixed-decimal point machine, with two keys [.->] and [<-.] that are used to set the decimal point position at any position from fifteen to zero digits behind the decimal point.