1. A computer program product comprising a tangible storage device having a computer readable program, wherein the computer readable program when executed on a computer causes the computer to: organize one read-only file system for a plurality of operating systems, each operating system executing on a distinct virtual machine, each virtual machine executing on the computer; organize a read/write file system for each operating system, each read/write file system comprising at least one pointer to the read-only file system, each read/write file system paired with the read-only file system appearing as a single, private file system to one respective operating system of the plurality of operating system; and access each read/write file system directly and the read-only file system through the at least one pointer from each respective operating system.