How GDGs base is created?

GDG base is created with the help of IDCAMS utility.

Syntax:

//GDGIDXX1 EXEC PGM=IDCAMS

//SYSPRINT DD SYSOUT=*

//SYSIN    DD *

    DEFINE GDG (NAME (SIMOTIME.DATA.GDGROUP1)   -

           LIMIT (3)                           -

           NOEMPTY                        -   (it deletes the oldest version)

           SCRATCH)