"To a large extent, the mainframe’s longevity is a result of two major architectural innovations first introduced with S/360. The first was the notion of a family of computers, from low to high performance, all based on the same instruction set which allowed customers to upgrade to larger systems as well as to future models without having to rewrite their applications. The second was OS/360, a common operating system that supported the various members of the S/360 family except for the smaller ones which ran a subset with more limited capabilities. Today’s z/Architecture and z/OS are direct descendants of the original S/360 and OS/360." --Irving Wladawsky-Berger, Wall Street Journal
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