Hardware-based address translation, or address translation is sort of an addition to limited direct execution.

Assumptions

• User’s address space is placed contiguously (连续地) in physical memory.
• The size of address space is less than physical memory.
• Each address space is of the same size.

Dynamic (hardware-based) relocation

Also referred to as base and bounds. (similar to esp and ebp?)

Physical address = virtual address + base

If a process tries to access address beyond bound, the CPU will raise an exception.

Base and bounds registers are in CPU (MMU).

OS issues

• When a process is created, OS finds space for its address space in memory.
• When a process is terminated, OS reclaims all its memory.
• When a context switch occurs, OS saves and restores different base-and-bound pairs.

If the OS wants to move a process not running, it copies its address space, and change its base and bound pair.