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> For example, MMUs are unnecessary if the OS verifies that all programs only access memory that's been allocated to it.

You'd need some sort of proof-carrying code to allow verification of these properties in binaries. Also, features like MMU's and interrupts are needed anyway to implement virtual memory, or user tasks with adjustable priorities.

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Would virtual memory still be necessary on a capability machine architecture [0] ? My understanding is that would not be the case since all programs can only access memory that's been allocated to it. By definition, capabilities cannot be created out of thin air like pointers can be ?

[0]: https://www.cl.cam.ac.uk/research/security/ctsrd/cheri/

You probably still want to use virtual memory to simplify the programming model (flat address space) and to be able to overallocate memory across many processes. Without virtual memory you are pushing these functionalities to app developers.

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