Mainframe, MVS and zOS Discussion

Hi,

What's the difference b/w create Data set and Catalog Data Set in ISPF 3.2? I'm not able to differentiate them, they seem to do the same thing. If not, can someone please help me to understand it.

Actually, they do not do the same thing at all. To understand the difference, however, you need to understand the purpose of the catalog. The catalog is a data set that contains data set names and volume serials -- along with a few other pieces of data -- but that is all. In order to actually use the data set, or find out much about it, you have to access the volume serial on which the data set resides.

It is possible for data sets to be created (tape OR disk) without being cataloged. In order to access such a data set, you MUST provide the data set name, the disposition (both just like for a cataloged data set) but you must also provide the volume serial and the unit (which come from the catalog when the data set is cataloged) -- four pieces of data instead of two. For a tape, you must also provide information about the label type and the sequence number (where the data set resides on the tape).

And for completeness, there is a master catalog and multiple user catalogs on a z/OS system -- the master catalog is identified during the IPL process and user catalogs are defined in the master catalog; most data sets will be defined in user catalogs although some system data sets will be defined in the master catalog. These details don't matter from an application programmer's viewpoint -- they only matter to system programmers.

Thanks Robert. It helps great!