If you have a need to restrict the program library block size to 1024 bytes you can specify that a maximum record size of 1024 bytes be used for the program library.

DC affects only load module contents, not program objects.

Specifying the DC attribute sets the block size for the program library data set to 1024 bytes with the following exception. For an existing data set, if the current block size is greater than 1024 bytes, the load module is written using a maximum record size of 1024 bytes; the block size in the DSCB entry for the data set is not changed.

DC=NO is the default value and can also be specified with the keyword NODC.