My understanding, from back then, was that VM/ESA 1.0 (so-called "370 edition") was a "mid-life kicker" to keep VM/SP and HPO customers happy, and allow them to migrate to VM/ESA, taking advantage of many of the small improvements on the CMS side, while still running on their older S/370 hardware, while waiting for IBM to deliver their shiny new S/390 machines.? IIRC, there was quite a long queue or "back-log of orders" of at least several months wait, from the time you ordered an upgrade to a 390, so this was a kind of "stepping stone" to help get the customers ready for the future, and made it easier to migrate the VM/ESA system from the 370 to the new 390, IIRC.
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