Abstract: One embodiment of the present invention provides a computer system with a plurality of storage memories, each storage memory storing an operating system program, and an identifier for identifying a storage memory containing an operating system program to be loaded when the unit is booted. The identifier is selectively switchable between storage memories so that the computer system may be selectively booted with an alternate operating system program. This facilitates loading a new version of an operating system, and then rapidly switching back to an old version of the operating system if the new version fails to function properly.