In 1968, Shima worked for Busicom in Japan, and did the logic design for a specialized CPU to be translated into three-chip custom chips.

In 1969, he worked with Intel's Ted Hoff and Stanley Mazor to reduce the three-chip Busicom proposal into a one-chip architecture.

With poor prospects for employment in the field of chemistry, he went to work for Busicom, a business calculator manufacturer, joining in Spring 1967.

Shima began work on a general-purpose LSI chipset in late 1968, and Busicom then approached the American companies Mostek and Intel for converting the logic into MOS circuits and the chip's layout for manufacturing.

The job was given to Intel, who back then was more of a memory company and had facilities to manufacture the high density silicon gate metal–oxide–semiconductor (MOS) chip Busicom required.

[7] This was then formulated by Intel's Marcian "Ted" Hoff in 1969, simplifying Shima's initial design down to four chips, including a one-chip CPU.

[5] Due to Hoff's formulation lacking key details, Shima came up with his own ideas to find solutions for its implementation.

They both eventually realized the 4-bit microprocessor concept, with the help of Intel's Stanley Mazor to interpret the ideas of Shima and Hoff.

Shima was responsible for adding a 10-bit static shift register to make it useful as a printer's buffer and keyboard interface, many improvements in the instruction set, making the random-access memory (RAM) organization suitable for a calculator, the memory address information transfer, the key program in an area of performance and program capacity, the functional specification, decimal computer idea, software, desktop calculator logic, real-time input/output (I/O) control, and data exchange instruction between the accumulator and general-purpose register.