ICM (International Calculating Machines) Model 816 Desktop Calculator

This machine is quite interesting, and appears to be fairly unusual. It was made by International Calculating Machines, of Woodland Hills, California, in the early 1971 timeframe. ICM was a consumer products subsidiary of the integrated circuit manufacturer Electronic Arrays(EA), located in Mountain View, CA. The ICM 816 was initially marketed at $450, quite expensive considering that by 1971, Sharp was selling the Large Scale Integration(LSI) IC-based QT-8D in the US marketplace for $395.

The nameplate for the "Senator Mini Calc" version of the ICM-816

Serial Number Tag for Caltype Senator Mini-Calc

Sometime during the '71-'72 timeframe, the ICM 816 (fully assembled by ICM, and ready to go) was sold under OEM contract to Caltype Corporation (a subsidiary of Transitron Corporation), of Los Angeles. Caltype marketed the ICM-816 as the "Senator Mini-Calc". The machine was identical to the original ICM-816, except for the name plate on the top cover of the machine which reads "Senator Mini-Calc; Made in USA", and the model/serial number tag, which replaced ICM's name with Caltype's. The model number of the machine listed on the model/serial number tag is still ICM-816, and the serial-numbering scheme follows ICM's method.

It is also very interesting to note that famous electronics manufacturer Sony, which entered the calculator marketplace in 1967, marketed a calculator called the ICC-88 beginning in fall of 1971 that utilized the same Electronic Arrays chipset as the ICM-816. The ICC-88 was Sony's first calculator to use non-Sony-made integrated circuits as the brains for the calculator. The display in the ICC-88 was a gas-discharge, seven segment planar display versus the Nixie-tube display of the ICM-816, and the Sony machine could operate on AC power, or through built-in rechargeable batteries. Otherwise, the ICM-816 and Sony's have the same features and operation.

In the early part of the 1970's, there was a dearth of upstart calculator manufacturers that were looking to try to grab a share of the market created by the dramatic decrease in price of calculating machine technology that larger-scale integrated circuits had made possible. At the time, IC technology was advancing very quickly, which made it difficult for the smaller players to keep up with big boys in the integrated circuit biz. Electronic Arrays fell upon hard times, and were later bought out by NEC Electronics in 1978. Along the rocky road to Electronic Arrays' failure and buyout, and about the time that the electronic calculator market suffered it's first big shakeout, the ICM subsidiary was liquidated. The remaining inventory of ICM calculators were later sold off through a surplus liquidator in San Jose, CA. ICM 816's were sold for as low as $135 each. If anyone out there knows anything more about ICM, or Electronic Arrays, I would love to hear from you.

Inside the ICM 816

The ICM 816 has much more than a passing similarity to another interesting and unusual machine in the museum, the Master H-1. The machines operate in a very similar manner, and in fact, share similar logic, both based on LSI chipsets made by Electronic Arrays. The ICM 816 seems to be a little earlier design than the Master H-1, as it uses a less-highly integrated six-chip LSI chipset rather than the four-chip set of the H-1. The chipset in the 816 is dated in early 1971, whereas the chipset in the Master H-1 is from late 1971 to early 1972. During this particular time in the development history of large scale integrated circuits, the time difference between the chips in the ICM 816 and the Master H-1 represents a long time, as LSI integrated circuit technology at the time was advancing at a break-neck pace. The 816 also uses older Nixie tube display technology rather than the early planar gas-discharge display panel used in the H-1.

Close-up View of ICM 816 Keyboard

As with the Master H-1, the ICM 816 uses an 8-digit display to provide 16 digits of integer capacity. A special key (a double-ended arrow, designated as [<->] in this text) on the keyboard toggles the display between the most and least significant eight digits of results which exceed eight digits. For example, multiplying 12345679 by 18 would result in "22222222" showing up on the display. The clue that there is more of the result to be displayed is that there is no decimal point in the display. (If the result were actually 22222222, it would be displayed as "22222222.".) Since there is no decimal point shown, pressing the [<->] key changes the display to "2 ", showing the least significant digit of the result. Subsequent presses of the [<->] key toggles the display back and forth between the most significant and least significant digits of the result. If there aren't any additional digits to be displayed, pressing the [<->] key results in a blanked display.

Though the ICM 816 and the Master H-1 share similar logic, there are some subtle differences in their operation. The ICM-816 will only allow entry of up to eight digits of input. If more than eight digits of entry are attempted, the machine goes into input overflow state, requiring a press of the [CE] or [C] key to clear the invalid entry. The Master H-1 allows input of up to 16 digits (with the least significant eight digits not visible to the user while they are being entered). Another subtle difference between the machines is that the Master H-1 ignores attempts to set the decimal point position to 8 or 9, wheras the ICM 816 seems to get somewhat confused by doing this.

The ICM 816 uses fixed decimal point logic, with a setting from zero through seven digits behind the decimal point. Setting the decimal point location is not intuitive, as there is no obvious switch or dial provided to make the setting. At power-up, the calculator defaults to zero digits behind the decimal point, making the machine effectively an integer-only calculator. Based on experience with the Master H-1, pressing and holding the [CE] key, while at the same time, pressing a digit from 0 to 7 on the keyboard, properly sets the fixed decimal point location. Pressing 8 or 9 as the decimal point position selection is accepted, but results in the machine blanking the display, and immediately causing an input overflow as soon as any non-zero digit is entered. This method of setting the fixed decimal point position is very much like that used on the Marchant Cogito 412 and Cogito 414 calculators.

Closer view of ICM 816 LSI's

The ICM 816 is based on a six-chip LSI chipset, with each ceramic-packaged chip having 24 pins. All of the chips are dated within the first few weeks of 1971. This chipset is a fairly early LSI calculator chipset, being preceded by the four-chip LSI chipset made by Rockwell for use in Sharp's QT-8D, the first calculator to utilize Large Scale Integration technology. The US Patent (Number 3,800,129) filed by Electronic Arrays to protect their technology indicates that the chipset is a microcoded CPU, utilizing ROM to provide the microcoded instructions that orchestrate the operation of other chips in the system to provide the brains for the calculator. The devices include an input chip (scan and encode keyboard), an output chip (multiplex and generate display), an arithmetic chip (perform logical and arithmetic operations), a register chip (provides working storage registers), and at least one (in this machine, it appears that two are used) program control chip (essentially, a ROM with microcode to control the the system). The chipset IC's are numbered "150-5001", "150-5004", "150-5005", "150-5013", "150-5014", and "150-5017". The machine's construction is of high quality, with individually replaceable kewswitch modules (using magnetic reed switches for reliability), high-quality silkscreened fiberglass circuit boards, and overall very durable construction.

The ICM 816 uses eight genuine Burroughs B5853ST Nixie tubes for its display. Each tube contains the digits zero through nine, and a right-hand decimal point. The display is driven by an unknown IC (no part number or other identification on it at all) in a 14-pin DIP package, as well as discrete transistor drivers. The display provides leading zero suppression, which is a feature that the Master H-1 does not provide. The Nixies sit behind a red filter that tints the orange Neon-glow display of the Nixies more toward the red end of the spectrum. Sign and overflow conditions are indicated by small discrete neon tubes located at the left (NEGative) and right (OVerFlow) ends of the bank of Nixie tubes.

The calculator is good about catching error conditions. Division by zero results in an immediate "OVF" condition, requiring a press of the Clear key to unlock the keyboard. Any result that would exceed the 16-digit integer capacity of the machine causes the "OVF" indicator to light and the keyboard to be locked out. Entry overflow (typing in more digits than the machine can handle) results in an overflow condition that can be cleared with the "CE" key.

The ICM 816 is fast calculator, with 99999999 divided by one requiring about a blink of an eye to complete. 99999999 squared (99999999 X 99999999) takes just a shade longer, but certainly less than 1/10th of a second.

The calculator in the museum is missing its model number plate, as evidenced by the rectangular area on the cabinet that has a significantly lighter color. This is where the nametag was placed. Apparently the adhesive failed over time, and the tag was lost.