The flat file database that wouldn't die
Now onto the true black hole of U.S. government IT: the IRS. For decades, the IRS held tax records in an Individual Master File, an enormous flat file containing millions of records, stored on big spinning wheels of magnetic tape, accessed via COBOL code.
Finally, in Janurary 2012, Customer Account Data Engine (CADE), a conventional database system run on IBM hardware, replaced Master File. And that switchover was only for data for individuals; business and retirement plans taxes are kept on the old system.
(Will paper returns also be a thing of the past? Don't hold your breath.)