How Apple Inc. became the most valuable company of all time

Why is Apple Inc. thriving while Facebook Inc. is diving? Watch a replay of a live video discussion with Times business reporter Walter Hamilton and columnist David Lazarus.

Apple became the most valuable company in history Monday while Facebook briefly fell to half its IPO price.

On an otherwise sleepy August day, Apple shares surged $17.04, or 2.6%, to $665.15 -- giving the company a market value of $623.5 billion. That tops the $620.6 billion that Microsoft Corp. touched briefly toward the end of the 1990s dot-com bubble.

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The rally has been paced by enthusiasm about the next generation iPhone, which is set to be unveiled Sept. 12.

Facebook, meanwhile, momentarily sank to less than half the price of its $38 initial public offering three months ago. The shares touched down at $18.75 before a rare rally carried the stock back above $20. It closed up 5% at $20.01.

The buying may have been paced by investors who jumped in once the share price had been cut in half.