A member of a PDSE can be updated in-place. Only one user can update at a time. When you update-in-place, you read records, process them, and write them back to their original positions without destroying the remaining records. The following rules apply:

• You must specify the UPDAT option in the OPEN macro to update the data set. To perform the update, you can use only the READ, WRITE, GET, PUTX, CHECK, NOTE, POINT, FIND, BLDL, and STOW macros.
• You cannot update concatenated PDSEs.
• You cannot delete any record or change its length; you cannot add new records.
• You cannot use LBI, large block interface.