An operating system from HP that runs on Alpha machines and HP's Itanium-based Integrity servers. OpenVMS was originally the VMS operating system from Digital Equipment for its very successful VAX line and later ported to the Alpha (originally from Digital) and Itanium CPUs (see VMS). Digital was acquired by Compaq and then HP. In 1991, VMS was renamed OpenVMS to reflect its Unix compliance (POSIX and XPG3 compliant) as the Unix environment was commonly known as "open systems" at that time. See POSIX.