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Back in 1996 John Young wrote a book "Exploring IBM's new-age mainframes". In it he talks about the improvements in underlying architecture, the improvements in the machine language set and he points towards the idea that the mainframe should be regarded as the central "super server" component of comprehensive networks. At the time the book was written the new internals for 64 bit addressing had not yet been released. I spoke to Bob Rogers at Poughkeepsie around that time about the 64 bit addressing that I had incorporated into Matrix. He had not at that time designed the internals to support it, and I simply incorporated a macro into my software generation set which performed 64 bit addressing, in anticipation that when it became a part of the internal structure of S/390, I would just include switches that took the architecture into account when generating the machine code. Since John's book came out much has changed, but almost all of it following on from the conceptions of that time. The mainframe can now incorporate many processors virtualizing any number of operating environments. This makes them ideal platforms for large, diversified workloads. There are probably no operating mainframes left that can only run one architecture, even though many users, especially the smaller ones continue to virtualize one single operating environment. The most popular of these being z/OS and z/VSE.