This is probably the second most common way to share a 3494 ATL or 3494 VTS when the 3494 is not actually partitioned. It is almost the same as having the 3494 partitioned, but gives the user more flexibility in terms of adjusting the size (number of volumes and/or number of devices) on each "side" without having to redefine the partitions. For basic operation, the CA TLMS supplied entry and eject exits will not need to be modified at all. However, if foreign tapes are going to be inserted into the 3494 and used on one of the systems; then a more complicated version of the entry exit will be needed.
For an example, we will assume that CPUA and CPUB share a 3494 with separate VMFs and TCDBs, and we want to allow foreign tapes to be used as input on CPUA. In this case, the entry and eject exits for CPUB would be unchanged. Since CPUA cartridges would be foreign to CPUB, when CPUB is notified that a CPUA cartridge has been inserted it would simply ignore it. Then, when CPUA was notified it would assign the correct status (SCRATCH or PRIVATE) and take ownership of the cartridge.
However, in the same example the entry exit on CPUA would have to be modified and it would be more complicated. In the CA TLMS supplied entry exit (CTSUXENT in the CAI.CTAPSAMP library), there would have to be code added at label RC16. If the volume being inserted is defined to CPUB (which means a table would need to be created or a set of compares would need to be done to see if the volser matches those defined to CPUB), then the instruction "LA R15,UXEIGNOR" would need to be performed (followed by the branch to EXIT). However, if the tape is not defined to CPUB (again, based on the volser) then you would want to branch to label RC8 (which would put the foreign tape into PRIVATE status and take ownership of it on CPUA). Depending on the volser standards on CPUB, this could be very simple (look for a cartridge starting with "B0" or "B1") or very complicated.
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