Masatoshi Shima (嶋 正利, Shima Masatoshi; born August 22, 1943, Shizuoka) is a Japanese electronics engineer. He helped create the world's first microprocessor, the Intel 4004. In 1968, Shima worked for Busicom in Japan. He designed the logic for a specialized CPU that would be made into three custom chips. In 1969, he worked with Intel's Ted Hoff and Stanley Mazor to change the three-chip Busicom plan into a single-chip design. In 1970, Federico Faggin created the Intel 4004 microprocessor using that design, with Shima helping with the logic design.

In 1972, Shima joined Intel. There, he worked with Faggin to develop the Intel 8080, which was released in 1974. Later, Shima created several Intel peripheral chips, some of which were used in the IBM PC. These included the 8259 interrupt controller, 8255 programmable peripheral interface chip, 8253 timer chip, 8257 direct memory access (DMA) chip, and 8251 serial communication USART chip. He then joined Zilog, where he worked with Faggin to develop the Zilog Z80 (1976) and Z8000 (1979).

Early life and career

He studied organic chemistry at Tohoku University in Sendai, Miyagi Prefecture, Japan. Because there were limited job opportunities in the field of chemistry, he began working for Busicom, a company that makes calculators, in Spring 1967. At Busicom, he learned about software and digital logic design from 1967 to 1968.

Intel 4004

In 1968, Busicom decided to use large-scale integration (LSI) circuits in their calculator products. This led to the start of the "Busicom Project," which aimed to create a chipset for the Busicom 141-PF calculator. This project eventually resulted in the development of the first microprocessor, the Intel 4004. In April 1968, Shima was asked to design the logic for a future chipset that would be created by a semiconductor company. Along with his supervisor, Tadashi Tanba, Shima designed a special-purpose LSI chipset in 1968. His design included seven LSI chips, such as a three-chip CPU. The design also featured arithmetic units (adders), multiplier units, registers, read-only memory, and a macro-instruction set to control a decimal computer system.

Busicom wanted to create a general-purpose LSI chipset for use in not only calculators but also other equipment like teller machines, cash registers, and billing machines. Shima began working on this general-purpose chipset in late 1968. Busicom then contacted American companies Mostek and Intel to help convert the logic into MOS circuits and prepare the chip for manufacturing. Intel was chosen for this task because it had the necessary facilities to produce the high-density silicon gate metal–oxide–semiconductor (MOS) chip required by Busicom.

In June 1969, Shima visited Intel to present his proposal. Because Intel lacked engineers who could understand the logic schematics or convert them, Shima was asked to simplify the design. Intel’s Marcian "Ted" Hoff simplified Shima’s initial plan into a design using four chips, including a one-chip CPU. Hoff’s version missed some important details, so Shima added his own ideas to solve problems during the implementation. Together with Hoff and with help from Intel’s Stanley Mazor, they developed the concept of a 4-bit microprocessor. Shima contributed by adding a 10-bit static shift register to support functions like a printer’s buffer and keyboard interface. He also improved the instruction set, made random-access memory (RAM) suitable for calculators, and refined other features such as memory address transfers, program performance, and data exchange between the accumulator and general-purpose registers.

The specifications for the four chips were developed over several months in 1969 by an Intel team led by Hoff and a Busicom team led by Shima. After returning to Japan in late 1969 and coming back to Intel in early 1970, Shima discovered that no progress had been made on the 4004 since his departure, and Hoff was no longer involved in the project. Federico Faggin, who had joined Intel just a week before Shima returned, became the new project leader. Faggin had previously worked at Fairchild Semiconductor, where he helped develop the MOS silicon gate technology needed to create the complex and fast 4004 chip. Shima worked with Faggin for six months, from April to October 1970, to finalize the logic design of the 4004 processor. Eventually, Busicom sold the rights to use the 4004 to Intel, except for its use in business calculators.

Intel 8080 to Zilog Z8000

After the 4004, Intel created the 8008 microprocessor. The 8008's architecture was designed by Computer Terminal Corporation, and its design was completed by Federico Faggin and Hal Feeney. In 1972, Shima joined Intel. He was hired to create the detailed design for Intel's next microprocessor, which became the Intel 8080. Federico Faggin was responsible for the 8080's concept and architecture. The Intel 8080 was released in 1974. After this, Shima developed several supporting chips for Intel, including the 8259 interrupt controller, 8255 parallel port chip, 8253 timer chip, 8257 DMA chip, and 8251 serial communication USART chip. Some of these chips were used in the IBM PC. Shima was not involved in the development of the Intel 8088 or 8086.

In 1975, Shima moved to Zilog. He worked with a small team to create the detailed design and physical layout of the Zilog Z80 microprocessor. Federico Faggin supervised this work and designed the Z80's architecture to be compatible with the Intel 8080's set of commands. Later, Shima completed the same task for the 16-bit Z8000 microprocessor.

According to Intel colleagues, Faggin's method involved designing logic directly at the transistor level, not at the gate or register level. This made the schematics difficult to read, but the way transistors were drawn helped with the physical layout of the chip. Shima explained that the logic was first tested on breadboards using transistor–transistor logic (TTL) chips before being translated into MOS transistor equivalents.

In 1980, Shima returned to Japan and started the Intel Japan Design Center. In 1986, he founded VM Technology Corporation. At VM, he developed the 16-bit microprocessor VM860 and the 32-bit microprocessor VM 8600 for the Japanese word processor market. In 2000, Shima became a professor at the University of Aizu.

Prizes

• 1997 Kyoto Prize in the field of advanced technology
• 2009 Fellow of the Computer History Museum for helping create the Intel 4004, the first commercial microprocessor in the world.