McKown, John wrote:
Depends on what you mean by a "real" difference. z/OS uses at least one instruction which is not implemented on an IFL as it is on a GP processor. That's why you will get a "check stop" condition if you IPL z/OS in an LPAR which is defined as using an IFL.
The instruction set supported by IFLs -- loaded at IML time -- deliberately leaves out one particular instruction that, while not all that important, does happen to be executed in the early IPL process for z/OS. That "trick" keeps z/OS from successfully IPLing on an IFL. That one instruction isn't used by Linux or by z/VM (or by various stand-alone utilities written by IBM or ISVs like Innovation and others) and so those operating systems and utilities IPL just fine. All of those operating systems and utilities run in both problem and supervisor state and use the full range of instructions and facilities available to any programs running in z/Architecture mode on a zSeries or z9 processor.
I agree that a problem program should see no differences. I was always curious if I could figure out a way to "cheat" to run COBOL on a zAAP somehow. But I don't have a zAAP to mess around with. And I don't run z/OS 1.7 either (isn't that were zAAPs are first supported?)
zAAPs are supported by z/OS 1.6.
But I will admit that I don't know exactly how different a zAAP is from a GCP. I just remember that some things will NOT work on a zAAP. I thought it was supervisory instructions and some types of interrupts.
zAAPs are (essentially) identical to GCPs. Only Java work is dispatched there and they are disabled from handling I/O interrupts. These are operating system choices for how zAAPs are handled. If the operating system chose to use them in other ways - i.e. dispatch other kinds of work there, it would work.
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