Toshiba continued with research and development of computers even after it withdrew from a joint project on TAC development with the University of Tokyo in 1956. However, no standard software such as an OS or utility was available on TAC-II and TAC-III, which were developed in the 1950s (neither was commercialized), and the user had to develop even the functions, usually provided by OS and utility on the modern computers, as a part of his/her application program on a case-by-case basis. In the 1960s, assemblers, loaders and compilers were finally developed and provided together with hardware (TOSBAC-3100 assembler in 1961, TOSBAC-4200 assembler/loader in 1962 and TOSBAC-4300 assembler/COBOL/FORTRAN/RPG in 1964).
TOSBAC-3400 in 1964 was the first Toshiba computer which was provided with OS. The history of Toshiba OS is divided into three stages. It, first, developed OSs for its computer products by itself, sometimes with joint research with the universities. Then, it decided to introduce technologies from the United States (license introduction), and, finally, resumed in-house OS development with ACOS-6 for upper models of the ACOS series77 in 1974.
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In-house OS Development
The first OS developed by Toshiba was TOPS-1 for TOSBAC-3400, completed in 1964. It was developed based on a FORTRAN monitor, which made up the FORTRAN system that had been jointly developed with Kyoto University in 1963. Subsequently, numerous OSs were developed for TOPS-3400, including TOPS-2, TOPS-4, TOPS-11, TOPS-14 and TMS. As their names suggest, these OSs constituted the TOPS series. However, each OS was individually developed in order to make the most of evolution of the hardware of TOSBAC-3400, and compatibility between them was not necessarily guaranteed.
The OS developed in-house after TOSBAC-3400 was “OS COS/MT” for TOSBAC-5100, announced in 1965. OS COS/MT was the OS for TOSBAC-5100 model 10. Subsequently, as models 20 and 30 were added to the TOSBAC-5100 series, COS/DS and COS/30 were developed, respectively, as the corresponding OSs. COS/DS and COS/30were equipped with database IDS. IDS had a network structured database in which interrelated records were linked with each other, and therefore was usually called a network-type database.
The following OS developed in-house was "ACOS-6", which was the last Toshiba’s mainframes. ACOS-6 was developed based on the technological ability cultivated through remodeling/enhancing “GCOS-3,” the OS for TOSBAC-5600 introduced from HIS (Honeywell Information Systems) of the United States under a technical agreement, as described in "2. Licensed OSs", for the Japanese market. For ACOS-6, a number of new functions were incorporated, such as a virtual memory system, robust memory access control with a domain protection function and a shared library function. In 1978, however, Toshiba withdrew from the mainframe business and transferred the business to former NEC-Toshiba Information Systems, Inc. (now NEC Total Integration Service Inc.), a joint venture company between Toshiba and NEC, pulling out of the development of ACOS-6 as a result. Toshiba has not developed another OS for mainframes.
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Licensed OSs
In 1964, during the time when Toshiba was developing OSs in-house, it signed a technical collaboration agreement on computers with General Electric (GE) of the United States with the aim of commercializing its computers for users in Japan by improving/enhancing them. The major licensed computers were the GE-400 and GE-600 series, which were commercialized as TOSBAC-5400 and TOSBAC-5600, respectively.
With TOSBAC-5400, GE and Toshiba initially introduced a magnetic tape-based uni-programming system called “MTPS”. Then, GE successively introduced various systems, including a full-scale multiprogramming system called DAPS based on a fixed magnetic disk device, DPS based on an removable magnetic disk pack that realized multiprogramming through parallelization of I/O processing and main unit processing, and a time-sharing system called TSPS based on the DPS. This technical collaboration with GE went beyond technology introduction through licensing. For example, it was found that the DAPS released by GE had drawbacks such as slow system startup and poor reliability of the fixed magnetic disk device. Toshiba independently modified the DAPS based on an removable magnetic disk pack device. Additionally, in 1970, Toshiba provided GE with an ALGOL compiler for TOSBAC-5400 that the company had developed independently.
Toshiba's aim in developing TOSBAC-5600 was to “Japanize” General Electric’s GE-600 series. However, in May 1970, GE sold its mainframe computer business to HIS (Honeywell Information Systems). The GE-600 series was renamed the H-6000 series, and Toshiba’s partner in the technical collaboration changed from GE to HIS. The OSs with which Toshiba had experience differed from one processing mode or hardware model (configuration) to another. However, the OS for the H-6000 series, “GCOS-3,” was based on an innovative concept of supporting the processing of local batches, remote batches, time sharing, remote access and transactions with a single OS.