The late 1980s and early 1990s saw big changes on the software side for Sequent. DYNIX was replaced by DYNIX/ptx, which was based on a merger of AT&T Corporation's UNIX System V and 4.2BSD. And this was during a period when Sequent's high-end systems became particularly successful due to a close working relationship with Oracle, specifically their high-end database servers. In 1993 they added the Symmetry 2000/x90 along with their ptx/Cluster software, which added various high availability features and introduced custom support for Oracle Parallel Server.