Architecture
CMS is an intrinsic part of the VM/CMS architecture, established with CP/CMS. Each CMS user has control over a private virtual machine – a simulated copy of the underlying physical computer – in which CMS runs as a stand-alone operating system. This approach has remained consistent through the years, and is based on:
- Full virtualization, used to create multiple independent virtual machines that each completely simulate the underlying hardware
- Paravirtualization, used to provide a hypervisor interface that CMS uses to access VM services; this is implemented by the non-virtualized DIAG (diagnose) instruction
More details on how CMS interacts with the virtual machine environment can be found in the VM and CP/CMS articles.
CMS was originally built as a stand-alone operating system, capable of running on a bare machine (though of course nobody would choose to do so). However, CMS can no longer run outside the VM environment, which provides the hypervisor interface needed for various critical functions.
Read more about this topic: Conversational Monitor System
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