This disclosure provides a computer system with operating system permitting dynamic reallocation of main memory during operation. In a particular embodiment the computer system with operating system are used in connection with non-volatile main memory stores (NMS) such as MRAM. As the NMS is a component of main memory attached directly to the memory bus, the NMS functions at substantially the same speed as traditional volatile memory stores. Reallocation of main memory and use of applications or programs stored on the inserted NMS occurs at speeds orders of magnitude greater than traditional secondary memory devices.