An abend, often capitalized as ABEND, is short for abnormal end and is a computer term used in reference to an abnormal end of task when running a software program. It is more commonly known as a crash or lockup, and usually causes the computer to become unresponsive. The term abend was originally used as an error message on IBM mainframe computers with the 360 operating system (OS), developed in the 1960s. Personal computers and more recently developed operating systems do not commonly use the term anymore, but the Novell Netware network OS still makes use of it in reference to software crashes and errors. This type of abnormal termination when running a program commonly indicates a problem with software rather than hardware, and usually means there is an error either in the software of an application or in the operating system.
The cause of an abend is usually faulty data or a flawed program instruction that the computer is not able to follow or is unable to recognize. For example, a software termination can occur if an instruction in the software program is pointing to an area of memory that the computer is not able to access. The result is an abend, and the computer will then lock up, also called freeze or hang. To become functional, the computer usually has to be rebooted, meaning it has to be turned off and back on again.
Newer operating systems are often more crash-proof than older ones. In case of a software problem, newer systems are often able to terminate only the flawed application, while leaving other applications unaffected. This makes it possible to recover from an abend in a software program without having to reboot the computer. Hardware problems are usually not the cause of abends, and will instead commonly cause a computer shut down or make it impossible to turn the computer on. Some hardware issues, like physical problems with a computer memory cell, can mimic the effects of an abnormal end of task.
IBM's 360 OS, where the term abend originated, was written in assembly language and was in use primarily between 1965 and 1972. This operating system was developed for mainframe computers, meaning large-scale, often room-sized computers that were mostly used for data processing by large companies and organizations. Today, the term abend is mostly used by computer hackers and computer programmers. It is also used by IT professionals and other users of the Novell Netware OS.