1. A method of supporting substantially simultaneous operation of a first operating system and a second operating system on a hardware arrangement, the first operating system comprising software that accesses a physical address space of a memory of the hardware arrangement, the second operating system comprising software that accesses the physical address space of the hardware arrangement wherein said first operating system and said second operating system comprises a driver for a direct memory access device, the method comprising: providing the first operating system direct access to the physical address space by using the driver when said first operating system executes on the hardware arrangement; providing the second operating system direct access to the physical address space by using the driver when said second operating system executes on the hardware arrangement; maintaining a first set of units of the physical address space to which the second operating system cannot access and a second set of units of the physical address space to which the first operating system cannot access; preventing access the physical address space when a request seeks to access a unit of the physical address space that is a member of either the first set or the second set according to whether said request originates from the first operating system or the second operating system wherein said act of preventing is accomplished without the need for remapping overlapping physical address spaces; and enforcing a policy of isolation between said first operating system and said second operating system by permitting said driver to directly control said device without virtualizing said device to said driver.