Difference between Library and PDS

Difference between Library and PDS I noticed that while allocating a dataset using 3.2 option we have different “Data set name type” which we can specify.  The allowable values I can see are the following  (LIBRARY, HFS, PDS, LARGE, BASIC,   EXTREQ, EXTPREF or blank)        I would give “PDS” for defining a PDS in my region. I have not used other values apart from PDS and BLANK. Can someone tell me what are the meaning of all the values for data name type mentioned It would be great if someone can list out the difference between library and PDS. To me they look similar. “; ; ; ;