Shares of Advanced Micro Devices Inc. rocketed 8.5% in active midday trade Friday to a 4 1/2-year high, and have now quadrupled in the past six months. With volume up to 56.4 million shares in afternoon trade, the stock was the most-actively traded on U.S. exchanges. The stock, which is on track to close at the highest level since April 20, 2012, had run up 5.4% on Thursday, after the chipmaker said its next-generation "Zen" chip achieved a 40% improvement in processor performance. The company was not immediately available for comment. Six months ago, the stock had closed at $1.91. Since then, AMD had reported quarterly results that surprisingly beat expectations--the first-quarter report triggered a 52% surge in the stock on April 22 while the second-quarter report sent the stock rallying 12% on July 22. Bearish investors have scrambled to close out their bearish as the stock rallies. Short interest has been cut nearly in half in the past six months, falling in July to the lowest level since May 2012.
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