A method and apparatus for reverting a disk drive to an earlier point in time is disclosed. Changes made to the drive are saved in a circular history buffer which includes the old data, the time it was replaced by new data, and the original location of the data. The circular history buffer may also be implemented by saving new data elements into new locations and leaving the old data elements in their original locations. References to the new data elements are mapped to the new location. The disk drive is reverted to an earlier point in time by replacing the new data elements with the original data elements retrieved from the history buffer, or in the case of the other embodiment, reads to the disk are mapped to the old data elements stilled stored in their original locations. The method and apparatus may be implemented as part of an operating system, or as a separate program, or in the controller for the disk drive. The method and apparatus are applicable to other forms of data storage as well. Also disclosed are method and apparatus for providing firewall protection to data in a data storage medium of a computer system.