What is an Abend

An abend is a software bug that causes a program to crash, particularly in a mainframe computer.

Breaking Down Abend

Abend, or AbEnd, is short for “abnormal end,” and comes from a time when programmers designed computer messages to be extremely short.

An abend has several possible root causes. Most common among them is an attempt to execute an invalid operation, such as attempting to access a memory space it has no authorization for.

The term abend for a program crash is a bit of a throwback. The IBM System/360, a mainframe computer, used the term in error messages following program crashes as far back as 1965. While it still appears from time to time in technical manuals, it is not a common word for program crashes in modern PC operating systems.

Abends on the New York Stock Exchange

Abend was a common word at the New York Stock Exchange (NYSE) in the 1970s when the IBM mainframe computers that recorded transactions would experience frequent software crashes. Trading would halt while technicians scrambled to reboot the systems. So frequent were these interruptions that the NYSE installed large-core storage to share memory among the primary computer system, a hot backup system and a warm backup system. As one system would suddenly go offline, the backup system would come on and, accessing the large-core storage, take over without losing a transaction.

Or that was the theory. In practice, corruption of LCS data would often cause the original abend in the primary system. As the backup systems would come online, they would crash from accessing the same corrupt LCS data. Eventually, the NYSE walled off the primary system from the backups to solve the problem.

The NYSE experienced a flashback to the abend days in 1998, when a hardware problem prompted the exchange to shut down trading for one hour. It was particularly bad timing, as the glitch came after the exchange spent approximately $2 billion upgrading their systems to draw listings away from the Nasdaq Stock Exchange. The NYSE’s only consolation was in the knowledge that the Nasdaq had twice previously shut down because a squirrel had sabotaged the system.

The NYSE shut down again in 2015 due to a glitch, this time for almost four hours. The exchange blamed the forced shutdown on abnormal activity following a software update. By this time, the Nasdaq had experienced two more embarrassing glitches, one during Facebook’s IPO in 2012, the other in 2013, when the security information processor failed and all Nasdaq-listed securities went offline for three hours. While accepting some responsibility for the glitch, the Nasdaq pointed the NYSE’s attempt to access the Nasdaq as an aggravating factor.