The following paragraph is from a longer sidebar to an article "The Beginning of I.T. Civilization – IBM’s System/360 Mainframe" by Mike Kahn that appeared in the 30 March 2004 issue of the Clipper Group's Captain's Log, page 4.
Not the Whole Story — Why Mainframe Software is Really the Crown Jewel
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There have been a number of series of operating systems for IBM’s mainframes – from the mainline original OS1 and OS2 to OS/MFT to OS/MVT to TSS to MVS to OS/390 to z/OS. The lineage carries the rights to the crown as the jewels of IBM’s Mainframe Empire. Almost of all of the black magic that other platforms’ operating systems hope to deliver under the banner of “mainframe-like” descend from this lineage. But there are other family lines in IBM’s royal family that have given us virtual machines and hypervisor control (VM and z/VM), scaled down functionality with greater operational simplicity (the original DOS to VSE to z/VSE), to large-scale transaction processing (TPF - primarily for airline reservation systems), and to several others developed outside of IBM (including MTS - Michigan Terminal System - from my college and early professional days).
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