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 a single 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; and access the read/write file system and read-only file system for each operating system, wherein the read/write file system and read-only file system appear to each operating system as a single, private file system and each read/write file system comprises at least one pointer to the read-only file system.