status of all components, switching control as necessary to maintain operations. There are also features designed into the software that allow programs to be written as continuously available programs. That is accomplished using a pair of processes where one process performs all the primary processing and the other serves as a "hot backup", receiving updates to data whenever the primary reaches a critical point in processing. Should the primary stop, the backup steps in to resume execution using the current transaction. The systems support relational database management systems like NonStop SQL and hierarchical databases such as Enscribe. Languages supported include Java, C, C++, COBOL, SCOBOL, Transaction Application Language (TAL), etc. It uses the scripting and job control language TACL. Hardware The HPE Integrity NonStop computers are a line of fault-tolerant, message-based server computers based on the Intel Xeon processor platform, and optimized for transaction processing. Average availability levels of 99.999% have been observed. NonStop systems feature a massively parallel processing (MPP) architecture and provide linear scalability. Each CPU runs its own copy of the OS, and systems can be expanded up to over 4000 CPUs. This is a shared-nothing architecture — a "share nothing" arrangement also known as loosely coupled multiprocessing, and no "diminishing returns" occur as more processors are added (see Amdahl's law). Due to the integrated hardware/software stack and a single system image for even the largest configurations, system management requirements for NonStop systems are rather low. In most deployments there is just a single production server, not a complex server farm. Most customers also have a backup server in a remote location for disaster recovery. There are standard products to keep the data of the production and the backup server in sync, for example, HPE's Remote Database Facility (RDF), hence there is fast takeover and little to no data loss also in a disaster situation with the production server being disabled or destroyed. HP also developed a data warehouse and business intelligence server line, HP Neoview, based on the NonStop line. It acted as a database server, providing NonStop OS and NonStop SQL, but lacked the transaction processing functionality of the original NonStop systems. The line was retired, and no longer marketed, as of January 24, 2011. See also Reliability engineering Tandem Advanced Command Language List of Computer Hardware Manufacturers References Sources Siewiorek, Daniel P.; Swarz, Robert S. (1998). Reliable Computer Systems, A K Peters, Ltd., .