isham research
IBM's Capacity Upgrade on Demand announcement 199-036 contains the following paragraph:
Notice to ISVs: IBM plans to discontinue its use of the version code field of the "Store CPU ID" instruction (STIDP) to identify the processor model for processors which have the Capacity Upgrade on Demand capability. With this announcement, ISVs are advised to use the new instruction, "Store System Information" (STSI) to obtain processor model and other related information for those processors.
This seems to say that any ISV products dependent on the STIDP instruction must be changed before the Capacity Upgrade on Demand capability is added to the IBM processor complex. In cases where ISV software is dependent on the contents of this field, it might otherwise cease to operate.
In fact, this isn't the true meaning at all. What it means is that IBM does not update the version code field when Capacity Upgrade on Demand is invoked. The value returned by STIDP is the one established by the last IML, and a true value for the upgraded system will be generated by the next IML.
Over the long term, the statement is true - the strategic direction is to use the STSI instruction as the STIDP instruction will cease to give meaningful information. The existing definition of the field returned by STIDP cannot cater for more than 15 LPARs or more than 16 processors in an LPAR.