The stock market crashed 30 years ago.

The Dow dropped 508 points on Oct. 19, 1987, what became known as Black Monday. The 22.6% decline remains its biggest ever.

Wednesday, the Dow Jones Industrial Average is experiencing a more auspicious event: finishing above 23000 for the first time. The stock market is eerily docile and major indexes are trading at a historically high level relative to expected earnings, leading some to worry that it is headed for a substantial pullback. However, few expect another 1987-style collapse.

Black Monday was in many regards emblematic of a new era for financial markets.

The selloff was driven in part by computer programs that automatically sold index futures when the market fell, exacerbating declines in the market. It was an early sign of the algorithm-driven trading that has since become prevalent on Wall Street.