High-frequency trading has hollowed out the stock market, where software code has replaced intuition and common sense.
The Dow Jones industrial average fell 179 points to 11010 as investors worried about Europe's ability to contain its debt crisis
Stocks add to gains after press briefing by president. With a surge of 200 points before falling back, Dow having its best day in three months as investors pile into stocks.
Hewlett-Packard's lowered forecast pulled the Dow down, to close about 68 points lower than the previous session. The Nasdaq barely gained, rising 0.90 points just before closing.
Stocks on the Dow gained Friday. But the Dow average closed lower for the week, which turned out to be tumultuous for stocks.