A modern computer operating system is altered to boot and run from a protected medium such as a CD-ROM. Files and configuration information are copied from a fully configured and operational OS to a hard drive image file. File system filters and device drivers are added that implement an emulated read-write hard disk drive by servicing initial read requests from the image file, and write requests and read requests to previously written data, from a written disk sector database. The OS is altered to load the filters and drivers during boot, and to subsequently run from the emulated read-write hard disk drive. The hard drive image file is then placed on a bootable protected medium.