1. A method to permit an application developer to decide the address space model to be supported by an operating system on a computer, the method comprising: selecting one of a mostly private address space (MPAS) model and a mostly global address space (MGAS) model, where if the MPAS model is selected, then a process is permitted to map a shared object in a mostly private address space (MPAS) layout so that the process perceives a behavior as if the process is running on a multiple address space operating system, and where if the MGAS model is selected, then the process is permitted to map a shared object in a mostly global address space (MGAS) layout so that the process perceives a behavior as if the process is running on a single address space operating system.