Applications that use the following interfaces must be checked and possibly updated to accommodate large format data sets. The application must also specify BLOCKTOKENSIZE=LARGE on the DCBE macro to indicate that it complies with the changes to these interfaces.

• The BSAM NOTE and POINT macros: these generally use a four-byte value (TTR0) for the relative track number. For large format data sets, these macros must use a TTTR value in the register instead, and will do so for all data sets when the BLOCKTOKENSIZE=LARGE parameter is set on the DCBE macro. You also can use BLOCKTOKENSIZE=LARGE with BPAM NOTE and POINT macros but the BLDL and STOW macros are unaffected by BLOCKTOKENSIZE.
• The number of tracks field (DEBNMTRK) in the data extent block (DEB): for large format data sets, the DEBNMTRK field contains the low order two bytes of the number of tracks and DEBNmTrkHi contains the high order byte.
• The DS1LSTAR field in the format 1 DSCB: this field contains the track number of the last used track. For large format data sets, an additional high order byte of the track number may be contained in the field DS1TTTHI, at offset X'68'.
• Track address conversion routines, which convert between relative (TTR) and absolute (MBBCCHHR) track addresses: these use a three-byte TTR value. For large format data sets, applications need to use these routines (pointed to by CVTPRLTV and CVTPCNVT) with new entry points at offset +12, which use a TTTR address value in register 0. See z/OS DFSMSdfp Advanced Servicesfor details about these conversion routines.