Partitioned Data Set Extended (PDSE) is a data set type that is managed by DFSMS. Externally, a PDSE is very similar to a PDS. Internally, the PDSE has a different directory structure, member format, and record format. A PDSE is indistinguishable from a PDS through most interfaces used to access a PDS directory or member. All ISPF functions support the PDSE.
You can concatenate a PDSE library with a PDS library if they have consistent record formats and logical record lengths. All functions in the Library Utility (option 3.1) support PDSEs with the exception of the compress function.