The maximum value for LIMIT when defining the GDG base is 255. The LIMIT determines how many generations can be accessed by relative access (i.e. 0, -1, -2,...-254, etc.). The settings for ERASE and SCRATCH determine what happens when the next cataloged dataset exceeds the specified LIMIT. With NOERASE and NOSCRATCH, the first cataloged dataset that exceeds the LIMIT will be "rolled out" of the Generation Data Group, but will still be cataloged, and the newest dataset "rolled in". With this setting, you can keep up to 9999 GDG datasets cataloged. Once generation 9999 is reached, the generation number rolls back to 0001.