Each user ran in a Virtual Machine under VM, an IBM hypervisor operating system. VM provided the virtual IBM 370 machine which the VPS operating system ran under. The VM code was modified to allow all the VPS virtual machines to share pages of storage with read and write access. VPS utilized a shared nucleus, as well as pages used to facilitate passing data from one VPS virtual machine to another. This organization is very similar to that of MVS; substituting Address Spaces for Virtual Machines.