Am I sure?
I'm no expert, although I have looked into the memory layout of RiscOS because I was interested.
It may be that over the different versions of RiscOS, new features were included, but Wikipedia indicates RiscOS 2 did not have virtual addressing, and I saw nothing in the remaining history to indicate that it was added later.
It is quite true that MEMC did have memory protection capabilities, but from what I have read, it was not used in the earlier versions of RiscOS, although I am sure that it was used in RISC iX.
I find it hard to believe that the current versions of RiscOS do not have memory protection, but my original post was really about RiscOS under Acorn's custodianship.