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Nippon Calculating Machine Co., Ltd. (Busicom) Busicom Model 120-DM Junior Desktop Calculator

The Nippon Calculating Machine Co., Ltd. (NCM) Busicom Junior, Model 120DM, was a desktop AC-powered electronic calculator that was made in two different versions, one that utilized an extremely efficient logic design that utilized 22 MOS small and medium-scale integrated circuits. The second design packed the logic of all of the 22 integrated circuits into a single MOS/LSI (Large Scale Integration) IC manufactured by fledgeling US chip maker Mostek under contract to NCM.

The Mostek MK 6010 Calculator on a Chip (Note NCM Logo on Chip Lid)

The chip that Mostek created for NCM was the first commercial "Calculator on a Chip", and was designated the MK-6010. This chip combined 360 logic gates and 160 flip-flops totalling 2,100 MOS transistors.

In appearance, the difference between the two versions of the Busicom Junior 120DM is that the first version was a bit thicker (approx. 1/2-inch) than the second version because the circuitry for the first version took three circuit boards stacked above each other versus a single circuit board for the second version. There are a number of known OEM customers of NCM that marketed the same calculators under their own brand name, including Sanwa Precisa in Japan, National Cash Register (NCR) in the US, and Elwro (Wrocławskie Zakłady Elektroniczne) in Poland. There may be others out there that have not yet been discovered.

All of the calculators have a very similar appearance with only variances in color and badging. The Old Calculator Museum is looking for any of the machines as listed below. If you have one of these calculators, working or not, please get in touch with the museum by clicking on the EMail button in the menu bar at the top of the page.

- NCM Busicom 120DM Junior (Version I)
- NCM Busicom 120DM Junior (Version II)
- Sanwa Precisa M-12 (Similar to Busicom Jr. Version I)
- Sanwa Precisa Sandiken SG-12 (Similar to Busicom Jr. Version I)
- NCR Model 18-15 (Similar to Busicom Jr. Version I)
- NCR Model 18-16 (Similar to Busicom Jr. Version II)
- Elwro (Wrocławskie Zakłady Elektroniczne, Poland) 105L (Similar to Busicom Jr. Version II)