It allowed installations to run OS/VS1 and MVS/XA simultaneously on the same machine, as guests of a third systemVM/XA. This way, the new MVS/XA system could be tested while the old production OS/VS1 system was still in use.
Systems were permitted to execute both OS/VS1 and MVS/XA simultaneously on the same hardware, with MVS/XA functioning as a guest of a third systemVM/XA. Consequently, the new MVS/XA could be tested while the existing OS/VS1 system remained in use.