To achieve the same total transaction throughput on a Sysplex multiple boxes would need to be used in parallel for each workload but a CICS address space, due to its semi-reentrant application programming model, could not exploit more than about 1.5 processors on one box at the time even with use of MVS sub-tasks. Without this, these customers would tend to move to the competitors rather than Sysplex as they scaled up the CICS workloads. There was considerable debate inside IBM as to whether the right approach would be to break upward compatibility for applications and move to a model like IMS/DC which was fully reentrant, or to extend the approach customers had adopted to more fully exploit a single mainframe's power using multi-region operation (MRO).