this may have taken place (though it would be more likely, I think, that extra backup processing power was
added to the system, rather than replacement.
The FT (Financial Times) ths morning, however, in the only reference I've seen so far, asserts that NYSE "Curbs" were placed on the market:
NYSE curbs fail to arrest Dow’s tumbleThe Dow Jones Industrial Average on Tuesday suffered its steepest one-day decline in more than five years as hedge funds and other traders of large blocks of shares struggled to cope with curbs put in place by the New York Stock Exchange. Those curbs were designed to encourage orderly trading.
Such so-called “circuit breakers” have been used by the US stock exchange during previous sharp market declines.
These can potentially bring trading to a halt. But because the worst of the plunge on Tuesday took place after 2.30 pm, the NYSE did not halt trading. Instead, at 1.03pm the NYSE introduced what it calls a trading collar. Such measures are introduced in the event of a 180-point decline in the NYSE composite index, and ensure that all large block orders of the S&P 500 stocks must be “stabilising” for the remainder of the day – meaning that they can take place only after an “up-tick” in the stock. It will be removed at the start of trading today, but it remained in place until the close of trading on Tuesday.
Trading collars can be removed if the index moves back to within 90 points of the previous day’s close, but that did not happen yesterday.
“Normally, when circuit breakers kick in to stop us from selling, we get a bounce,” one trader said. “However, a whole queue of sell orders hit the system. That is not a good omen when the circuit breakers do not bring us back. We dropped in a matter of minutes. This is not supposed to happen.”
/...
Nevertheless, the trigger was the Chinese Govt's attempts to cool down China's very bubbly, overheating stockmarkets, in the context of very high levels, increasing weakness and, let's say, "irrational exuberance" in markets all around the world (except, perhaps, to a lesser degree, in Europe).
Greenspin's "recessionary" remarks on the US economy the other day certainly didn't help much; and Bernanke's Fed and Bush's Admin have a great deal to answer for provoking/promoting such a false, overly-liquid economy.