Recently I learned the hard way that IBM Enterprise COBOL compiler cannot generate 8-byte long POINTER variables, but only 4-byte pointers, meaning, that you cannot use more than 2GB in COBOL on a mainframe. I.e., you cannot make use of AMODE=64 with COBOL on the mainframe. You can run in AMODE=64, but you cannot exploit it. BTW, we have the year 2013. So, no big-data on mainframe with COBOL.
IBM Assembler and C/C++ can fully exploit AMODE=64, i.e., can use 8-byte long pointers.