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NCR 18-16 / Busicom Junior

This page features the NCR 18-16 (also known as the Busicom Junior), which was the first calculator to use a single "calculator on a chip" integrated circuit. This was developed from the NCR 18-15, which is illustrated at the bottom of the page, which uses 22 integrated circuits and was necessarily slightly larger.

NCR 18-16

NCR 18-16  (a re-badged Busicom Junior)

Display is 12 digits, separate green vacuum-fluorescent tubes.

4 functions.

The first use of a "Calculator on a Chip": the Mostek MK-6010 LSI (Large Scale Integration) chip, here date coded mid-1971.

160 x 275 x 85 mm (6.25" x 11" x 3.5"), 1600 g (3.5 lbs).

Introduced late 1970-early 1971.

Made in Japan by Busicom Corporation for NCR (National Cash Register).

This is a development of the NCR 18-15, see below.

Price of the Busicom Junior version, in UK in 1971, 168 Sterling (about US$400).

Inside NCR 18-16

Inside - compare with the previous model the NCR 18-15, below.

LSI chip

The circuit board showing the single Mostek LSI chip mounted on a plug-in chip carrier.

Mostek MK6010

Cutting edge technology of 1971, the Mostek MK6010 "calculator on a chip". The integrated circuit illustrated is date coded 7125 (i.e. 1971, week 25) and is also marked with the NCM (Nippon Calculating Machines) logo.

The IC is mounted on a small piece of circuit board which plugs sideways into the black socket.

"Calculator on a Chip"

The magazine "Electronics" for Feb 1st. 1971 says[1]:

"Mostek produced the first calculator on a chip for Busicom Corp. The 180-mil-square [0.18 inches-square (4.6 mm-square)] chip contains the logic for a four function 12-digit calculator - more than 2,100 transistors in 360 gates plus 160 flip-flops. Busicom's initial use of the chip will be as a direct replacement in its Junior model calculator now being distributed in the U.S. by National Cash Register."

Chip replaces circuit boards

The chip held in the hand replaces the two circuit boards full of components, including 22 MSI (Medium Scale Integration) integrated circuits, see article below and the NCR 18-15 below.

The single chip, using a p-channel process, replaced 22 chips in the previous version of this Busicom Junior calculator, see below, and reduced the number of circuit boards from two to one. Note that separate transistors are still needed as high-voltage display drivers.

The article continues ... "The original calculator's discrete diode-resistor and IC logic was a very clever design, says Mostek, developed over many years and requiring nearly the minimum logic necessary for a four-function machine. ... the minimised logic contributed greatly to Mostek's success in putting a calculator on a single chip".

Mostek of Dallas was then less than 2 years old. For more information about Mostek visit the MostekLives site.


This was the first use ever of a single chip for all the functions of a calculator, described then as a "Calculator on a Chip". It was the cutting-edge technology of the day .

This was the culmination of the gradually increasing integration during the late 1960s, accompanied by reducing number of components. Driving the display required higher power transistors which could not be easily integrated with the logic circuits on the chip, but within a couple of years this was achieved and the only electronics required for a simple calculator was the one chip.

The reduction of the calculator logic to a single chip had two immediate effects:

  • The calculator could now be much smaller and consumed much less power, leading on to small pocket calculators (eg. the Busicom Handy LE-120).
  • Assembly was much simpler so low labour costs were not so important and many manufacturers appeared in the U.S.A. and Europe. A few years later, when the cost of the chip, display, and keyboard had dramatically fallen, the assembly cost again became a large proportion of the total cost and manufacture returned to low labour-cost countries.

The development of electronics had now reached the stage at which a truly pocket-sized calculator was possible.


NCR 18-15

NCR 18-15

NCR 18-15

Display is 12 digits, separate green vacuum-fluorescent tubes.

4 functions.

Semiconductors: 22 integrated circuits, from Mitsubishi, Toshiba, and NEC, here date-coded 1970, and 260 diodes.

160 x 275 x 97 mm (6.25" x 11" x 3.8") - this is slightly larger than the NCR 18-16, above.

Made in Japan by Busicom Corporation for NCR (National Cash Register).

The NCR 18-15 is the immediate predecessor of the NCR 18-16 above. Although looking roughly the same, the NCR 18-15 is actually 12mm (0.5") thicker to accomodate the three circuit boards against the single board of the NCR 18-16.


Inside the NCR 18-15, with, on the right, the two large circuit boards and the small display boards.

Top board
Bottom board

The upper circuit board of the NCR 18-15.

The lower circuit board of the NCR 18-15.


  1. "Single-chip calculator hits the finish line", Electronics, Feb. 1 1971, pp19-20.
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