Developer | IBM / National CSS |
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Working state | Historic |
Initial release | 1968 |
Platforms | IBM System/360-67, System/370 |
Preceded by | CP/CMS |
History of IBM mainframe operating systems |
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VP/CSS was a time-sharing operating system developed by National CSS. It began life in 1968 as a copy of IBM's CP/CMS, which at the time was distributed to IBM customers at no charge, in source code form, without support, as part of the IBM Type-III Library. Through extensive in-house development, in what today would be termed a software fork, National CSS took VP/CSS in a different direction from CP/CMS. Although the two systems would eventually share many capabilities, their technical implementations diverged in substantive ways.
VP/CSS ran on IBM and IBM plug compatible hardware owned by NCSS (and by a few customers with site licenses, including Bank of America and Standard Oil of California). After an initial period running on the IBM System/360-67 platform used by CP/CMS, VP/CSS was ported to the System/370 series, made possible when IBM added virtual memory capabilities to the S/370 series in 1972.
VP/CSS was notable for supporting very large numbers of interactive users per machine, when compared with other IBM mainframe operating systems. Technical, operations, and commercial factors all played a role in making National CSS a commercially viable service business.
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