Method for Using Embedded Free Space on a Disk or Diskette
Original Publication Date: 1985-Mar-01
Included in the Prior Art Database: 2005-Feb-18
A method is described for keeping track of embedded free space on a disk or diskette when the operating system, e.g., Microsoft DOS, does not allow records to be freed from the file except by deleting all the data in the dataset. Since space is allocated to a dataset by the operating system, as logical records, i.e., logically contiguous sectors, are freed up, because of record deletions or size change, they are not returned to a free sector pool to be reused. Logical sectors allocated to a dataset but currently unused by valid records may be reused if the following method is employed. At the time the dataset is opened, the storage access method reads the index nodes on the media and builds a map of all sectors currently allocated to the dataset by the operating system and currently in use by valid records in the index.