The next issue on the list was the ISA which moves from a 32-bit one on the prototype to a full 64-bit version in the Shasta/Mojave pair. SM can run what it calls personalities in software but they are not implemented in the expected way. Personalities are software and are loaded at boot time, but they are both light and low-level. They don’t emulate code, they just translate it to the native ISA, a 32-bit add is a 32-bit add on both native and emulated hardware, but probably have differing opcodes. Occasionally this software will need to do something more complex but the bulk of the work is basically a big lookup table.
Personalities are not purely software though, there are hardware hooks to assist in with the job, unfortunately SM did not go into more detail here. One thing they did say is that the code is not user accessible and runs underneath everything including a hypervisor where applicable. In x86 terms, think of this as ring -2 or something similar. To running code and users, everything should appear to be native hardware, assuming it all works as promised.
