All PDSE space is available for either directory or member use. Within a data set, there is no difference between pages used for the directory and pages used for members. As the data set grows, the members and directory have the same space available for use. The directory, or parts of it, can be in secondary extents.

Directory pages are no longer a factor in determining space requirements. A PDSE does not have preallocated, unused, directory pages. Directory space is automatically expanded as needed.

The format of a PDSE lets the directory contain more information. This information can take more space than a PDS directory block.

The PDSE directory contains keys (member names) in a compressed format. The insertion or deletion of new keys may cause the compression of other directory keys to change. Therefore the change in the directory size may be different than the size of the inserted or deleted record.