Operating systems that supported Alpha included OpenVMS (previously known as OpenVMS AXP), Tru64 UNIX (previously known as DEC OSF/1 AXP and Digital UNIX), and Windows NT (until 4.0 SP6 and Windows 2000 RC1). Open source operating systems that run on the Alpha are Linux (Debian, Gentoo Linux and Red Hat Linux), BSD UNIX (NetBSD, OpenBSD and FreeBSD up to 6.x) and L4Ka::Pistachio.