state. Due to the fact that the CLI is loaded into the same address space as user code, and that the CLI is responsible for invoking image activation and image rundown, the CLI is mapped into the process address space at supervisor access mode - a higher level of privilege than most user code. This is in order to prevent accidental or malicious manipulation of the CLI's code and data structures by user mode code. Features Clustering OpenVMS supports clustering (first called VAXcluster and later VMScluster), where multiple computers run their own instance of the operating system. Clustered computers (nodes) may be fully independent from each other, or they may share devices like disk drives and printers. Communication across nodes provides a single system image abstraction. Nodes may be connected to each other via a proprietary hardware connection called Cluster Interconnect or via a standard Ethernet LAN. OpenVMS supports up to 96 nodes in a single cluster. It also allows mixed-architecture clusters. (VAX, Alpha, and Itanium computers each have a different architecture.) OpenVMS clusters allow applications to function during planned or unplanned outages. Planned outages include hardware and software upgrades. Networking The DECnet protocol suite is tightly integrated into VMS, allowing remote logins, as well as transparent access to files, printers and other resources on VMS systems over a network. Modern versions of VMS support both the traditional Phase IV DECnet protocol, as well as the OSI-compatible Phase V (also known as DECnet-Plus). Support for TCP/IP is provided by the optional TCP/IP Services for OpenVMS layered product (originally known as the VMS/ULTRIX Connection, then as the ULTRIX Communications Extensions or UCX). TCP/IP Services is based on a port of the BSD network stack to OpenVMS, along with support for common protocols such as SSH, DHCP, FTP and SMTP. DEC sold a software package named PATHWORKS (originally known as the Personal Computer Systems Architecture or PCSA) which allowed personal computers running MS-DOS, Microsoft Windows or OS/2, or the Apple Macintosh to serve as a terminal for VMS systems, or to use VMS systems as a file or print server. PATHWORKS was later renamed to Advanced Server for OpenVMS, and was eventually replaced with a VMS port of Samba at the time of the Itanium port. DEC provided the Local Area Transport (LAT) protocol which allowed remote terminals and printers to be attached to a VMS system through a terminal server such