11. What is a Generation Data Group (GDG)?
Generation Data Group is a group of chronologically or functionally related datasets. GDGs are processed periodically, often by adding a new generation, retaining previous generations, and sometimes discarding the oldest generation.

12. How is a GDG base created?
A GDG base is created in the system catalog and keeps track of the generation numbers used for datasets in the group. IDCAMS utility is used to define the GDG base.

13. When should DISP=MOD is used?
DISP=MOD is used to either extend an existing sequential dataset or to create a dataset if it does not exist. If the dataset exists, then records are appended to the dataset at the end of the existing dataset. If the dataset does not exist, the system treats MOD as if it were NEW, provided that the volume parameter has not been used.

14. What is the difference between the JOBLIB and the STEPLIB statements?

JOBLIB is defined at the start of the job before any EXEC and contains the load libraries to be searched for the entire job. STEPLIB is defined after an EXEC and applies only to that step. It also contains the load libraries to be searched for the step. JCLLIB is defined at the start of the job before any EXEC and contains the procedure (JCL) libraries to be searched for any procedures (that is, anything not EXEC PGM=) or INCLUDE members.

15. Name some of the JCL statements that are not allowed in procs.?
JOB, Delimiter(/*), or Null statements, JOBLIB or JOBCAT DD statements, DD * or DATA statements and Any JES2 or JES3 control statements.

16. How many extents are possible for a sequential file ? For a VSAM file?
16 extents on a volume for a sequential file and 123 for a VSAM file.

17. What does a disposition of (NEW,CATLG,DELETE) mean?
This is a new dataset and needs to be allocated, to CATLG the dataset if the step is successful and to delete the dataset if the step abends.

18. What does a disposition of (NEW,CATLG,KEEP) mean?
This is a new dataset and needs to be allocated, to CATLG the dataset if the step is successful and to KEEP but not CATLG the dataset if the step abends. Thus if the step abends, the dataset would not be catalogued and we would need to supply the vol. ser the next time we refer to it.

19. What is DISP=(NEW,PASS,DELETE)?
This is a new file and create it, if the step terminates normally, pass it to the subsequent steps and if step abends, delete it. This dataset will not exist beyond the JCL.

20. What is 'S0C7' abend?
Caused by invalid data in a numeric field.