Both the individual and business master files are still written in IBM mainframe assembly language, and are circa 56 years old. See the table on page 4 of this PDF for a list of the oldest systems in operation:
Number three on the the list is The DoD's Strategic Automated Command and Control System, which runs on "an IBM Series/1 Computer—a 1970s computing system—and uses 8-inch floppy disks". No biggie; it just "coordinates the operational functions of the United States’ nuclear forces, such as intercontinental ballistic missiles, nuclear bombers, and tanker support aircrafts."
> Standard CFOL Access Protocol (SCAP) is written in COBOL/Customer Information Control
System (CICS). SCAP downloads Corporate Files On-Line (CFOL) data from the IBM mainframe at
the Enterprise Computing Center, Martinsburg. The CFOL data resides in a variety of formats
(packed decimal, 7074, DB2, etc.)
https://oversight.house.gov/wp-content/uploads/2016/05/2016-...
Number three on the the list is The DoD's Strategic Automated Command and Control System, which runs on "an IBM Series/1 Computer—a 1970s computing system—and uses 8-inch floppy disks". No biggie; it just "coordinates the operational functions of the United States’ nuclear forces, such as intercontinental ballistic missiles, nuclear bombers, and tanker support aircrafts."