Miyagi Yoshio was born on November 18, 1928. Upon graduating from the Department of Communication Engineering, School of Engineering of Tohoku University in 1952, he joined NEC Corporation, and was assigned as an engineer of the Cable Carrier Transmission Division.

In 1957 when it became viable to use the Ge-alloy-junction-transistor for communications equipment, Miyagi engaged in a study of the transistor logic circuits, and developed an automatic error correcting telegraph system in 1958, which were delivered to the Japan Defense Agency, Sumitomo Metal Industries and others. Since integrated data processing using punched card system (PCS) was commonplace in those days in Japan, improvement in the technology for the data transmission among remote terminals was a serious issue.

Based on the technologies of the transistor computer ETL Mark IV developed in the ElectroTechnical Laboratory (ETL) of the Ministry of International Trade and Industry (MITI), NEC developed the NEAC-2201 and installed it in the computation center of the Japan Electronic Industries Development Association (JEIDA) in September 1958. It was the first "general purpose computer" by NEC. Miyagi, together with Aoyama Nariyuki, Shimaya Kazunori, Kitamura Takuro and others, participated in the design of this computer under the direction of Kaneda Hiromu. From then, Miyagi had been in the forefront of computer development in our country until his retirement from NEC.

Based on the experiences of this NEAC 2201 development, Miyagi and his fellows started the design of NEAC 2203, and completed it the next year, in 1959. The NEAC 2203, whose main memory consisted partly of magnetic core memory, was a practical business data processing system. The system comprised of magnetic tape memory units, large capacity magnetic drum memory units, punched card input/output units, and line-printers, and had the ability of multiplex operation of these peripheral units. The amount of sales orders received for the NEAC 2203 at the end of FY1960 was 23 systems, totaling 1.5 billion yen, which was a surprising amount in those days. For this success, he, together with Kaneda, received a Technical Development Award of the Academic Promotion Awards from the Institute of Electrical Engineers of Japan (IEEJ) in May 1961.

Furthermore, in February 1962, Miyagi completed the NEAC 2206, improving its performance remarkably by introducing Si-Mesa transistors for its logic circuits, adopting magnetic core for its main memory, and other innovations. He received a degree of Doctor of Engineering from the Tohoku University in February 1962 for his research regarding these computer technologies.

In 1964, Miyagi began the study of integrated circuit technologies for computer use, attaining to the development of NEAC 2200/500, the world's first large scale computer system fully consisting of monolithic ICs, and installed it in the Computer Center of Osaka University in 1966. He continued to pursue the development of super high speed computer technologies, and completed the NEAC 2200/700, which was installed at the Tohoku University in 1970.
Participating in MITI's "Ultra-High Performance Computing Project" in 1966-1971, Miyagi succeeded in the development of an NMOS LSI high speed memory for cache memory. It was the time to enter a new era of LSI computer in the 1970's.

Until Miyagi left NEC's computer technology development division in 1979, he led developments of LSI computer technologies, the new computer series ACOS77, NTT's DIPS computers, and other projects. After that, he contributed to NEC's computer technology as the president of NEC Engineering Corporation (1984-1994). At the Information Processing Society of Japan (ISPJ), he served as a director during 1980-1981.