In a system without virtual address mapping, it is harder to create a separation among sections that can be accessed by the software at runtime. The memory protection unit, often referred to as the MPU, is an optional component present in many ARM-based microcontrollers. The MPU is used to separate sections in memory by setting local permissions and attributes. This mechanism has several uses in real-life scenarios, such as preventing access to the memory when the CPU is running in user mode, or preventing fetching code to execute from writable locations in RAM. When the MPU is enabled, it enforces the rules by triggering a memory exception interrupt when those are violated.

While commonly used by operating systems to create process stack separation and enforce privileged access to system memory, the MPU can be useful in a number of other cases, including bare-metal applications.