NonStop is a series of servers introduced by Tandem Computers Inc., beginning with the NonStop product line , which is followed by the Hewlett-Packard Integrity NonStop product line extension . Because NonStop systems are based on an integrated hardware / software stack, HP also has 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 almost only redundant components. When a mainline component fails, the system automatically falls back to the backup.
These systems are Often used by banks , exchanges Stock , 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 Itaniummicroprocessors (TNS / E), was introduced. In 2014, the first systems “NonStop X” (or TNS / 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 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 code which runs atop this layer, which implements a Unix-like interface for other components of the OS to use. 
The operating system and application are both designed to support the fault tolerant hardware. The operating system continually monitors the status of all components, switching control as necessary to maintain operations. There are also features in the software that allow programs to be implemented. That is accomplished using a “hot backup” approach, which is accomplished in a “hot backup” manner. Should the primary stop, the backup steps in the process of execution using the current transaction. 
The systems supporting relational database management systems like NonStop SQL and hierarchical databases Such As Enscribe . 
The HP Integrity NonStop computers are a line of fault-tolerant servers based on the Intel Itanium processor platform, and optimized for transaction processing. Average availability levels of 99.999% have been observed.  NonStop systems feature massively parallel processing (MPP) architecture and linear scalability. Each CPU can be expanded to over 4000 CPUs. This is a shared nothing architecture – a “share nothing” arrangement also known as loosely coupled multiprocessing , and no “diminishing returns” (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 many other aspects of the production of this product, and the result is that it can be used in many situations.
HP also developed a data warehouse and business intelligence server line, HP Neoview , based on the NonStop line. It provides a database server , providing NonStop OS and NonStop SQL , but lacks the transaction processingfunctionality of the original NonStop systems. The line was retired , and no longer marketed , as of January 24, 2011. 
- Reliability engineering
- Tandem Computers
- Tandem Advanced Command Language
- ^ Jump up to:a b “HP NonStop for Dummies” . Wiley Inc. September 2014.
- Jump up^ HP NonStop Server Security: A Practical Handbook . Digital Press. ISBN 978-1555583149 .
- Jump up^ “Compare system availability in the real world” . Hewlett-Packard. October 2006 . Retrieved 2010-08-07 .
- Jump up^ Morgan, Timothy Prickett,The Register “HP euthanizes Neoview data warehouse iron: Itanium death”,The Register, Hardware, 24th January 2011