Tru64 (not True64), which was originally DUnix (Digital Unix), is based on OSF/1 and is a 64-bit operating system. It was used and found on the Digital (Alpha) DEC platforms. Today, Tru64 is a product and trademark of Hewlett-Packard.
Note: HP announced that Tru64 would stop being sold on October 1, 2012. Support ended on December 31, 2012.