Abstract: A data storage medium having the ability to recover from media errors includes a directory located at any desired region of a data storage area with redundant directory pointers at reserved locations. A unique file token is included in the directory entry for each data file and is also included in each extent list where the locations of parts of a fragmented data file are stored. Multiple extent lists are chained in two directions to facilitate reconstruction of the chain if part of the pointer information is lost.

Abstract: A removable optical disk of the write once type is managed to minimize size of the control area for user data recorded on the disk. Instead of recording each recorded file indicating token (serial number) as each file is recorded, a maximum value file token having a numerical value greater than a previous maximum value token is recorded in the control area such that any optical recorder receiving the disk may start recording data using such maximum value token. If the file indicating token values reach the maximum value token, then a new maximum value token is created. A pseudo end of volume (EOV) value is maintained which points to a one of the addressable data storing ares of the disk which is allocated and not recorded as EOV. All allocated data storing areas with addresses greater than EOV are recorded in contiguously addressed data storing areas. When any data storing area having an address higher than EOV is left unrecorded, then EOV is updated to point to that unrecorded allocated data storing area.

Abstract: A WORM data storage medium includes primary and secondary data storage areas in which data and pointers to allocated but unwritten update areas are written. Original and updated data is written in a write sequence or chain of primary data areas separated by branched secondary data storage areas. The most recent updated data is found in a two level search of primary and then secondary data storage areas in order to save time by searching only those secondary areas where the most recent update exist.