In a word, growth. Unexpectedly high demand keeps overloading systems pieced together without sufficient testing, say analysts and companies that run the sites. There's been no shortage of such problems. For example, auctioneer EBay froze out bidders for hours on May 3 and May 20.
Companies can quickly outgrow their technologies in a very short period of time.
Schwab attributes its crashes to complicated interactions between software and hardware, including mainframe computers. By December, that number grew to 100,000. To meet demand, Schwab is working closely with Cisco, IBM, and Sun to build a system that can handle 200,000 simultaneous trades and will include a duplicate data center that can come online instantly if the primary one fails, according to Gordon. Schwab will also add phone representatives and beef up the capacity of its automated phone system. And it's running an ad campaign aimed to let customers know some of the limits of online trading.