NonStop

NonStop is a series of server computers introduced to market in 1976 by Tandem Computers Inc., beginning with the NonStop product line, which was followed by the Hewlett-Packard Integrity NonStop product line extension. Because NonStop systems are based on an integrated hardware/software stack, HP also developed a special operating system for them: NonStop OS.

NonStop systems are, to an extent, self-healing. To circumvent single points of failure, they are equipped with some redundant components. When a mainline component fails, the system automatically falls back to the backup.

These systems are often used by banks, , telecommunication providers and other enterprises requiring extremely high uptime.

Originally introduced in 1976 by Tandem Computers Inc., the line was later owned by Compaq (from 1997) and Hewlett-Packard (since 2003). In 2005, the current product line of HP Integrity NonStop servers, based on Intel Itanium microprocessors, was introduced. In 2014, the first systems "NonStop X" running on the Intel X86 chip were introduced.

Early NonStop applications had to be specifically coded for fault-tolerance. That requirement was removed in 1983 with the introduction of the Transaction Monitoring Facility (TMF), which handles the various aspects of fault tolerance on the system level.

NonStop OS is a message-based operating system designed for fault tolerance. It works with process pairs and ensures that backup processes on redundant CPUs take over in case of a process or CPU failure. Data integrity is maintained during those takeovers; no transactions or data are lost or corrupted.

The operating system as a whole is branded NonStop OS and includes the Guardian layer, which is a low-level component of the operating system and the so-called OSS personality which runs atop this layer, which implements a Unix-like interface for other components of the OS to use.

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