Address translation can do more than choose where memory lives. Each mapping can also describe which accesses are permitted.

Page permissions

A page can be marked readable, writable or executable. It can also be restricted to privileged execution.

When a memory access violates the mapping, the processor raises an exception instead of completing the access.

Process isolation

Different processes normally have different page tables. A virtual address in one process therefore does not provide direct access to another process's private memory.

The kernel changes the active address-space context and controls which mappings exist. This combines software policy with hardware enforcement.

Page faults

A page fault is the exception raised when translation cannot satisfy an access. Some faults indicate an invalid operation; others let the operating system create or load a valid mapping and resume execution.

Memory protection is therefore not a convention that applications agree to follow. The processor's translation and privilege mechanisms actively enforce the boundary.