Shares of Apple reached $600 for the first time on Thursday, setting yet another milestone for the stock market's most valuable company. The stock hit $600 moments after the market's open before falling back below that level in early morning trading. Apple's (AAPL, Fortune 500) stock price growth has risen for the past three years, boosted in particular by record sales of the iPhone and iPad. The much-hyped third-generation iPad is set to go on sale Friday. It was almost exactly one month ago that Apple cracked the $500 level for the first time. Apple passed the $400 level for the first time seven months earlier, and it's been just 17 months since it passed $300. Shares traded above $200 for the first time in October 2009. At $600, the combined value of Apple's outstanding shares is more than $559 billion, the third-highest valuation ever for a public company. It now only trails General Electric (GE, Fortune 500) and Microsoft (MSFT, Fortune 500), which both soared to around $600 billion during the dot-com bubble at the turn of the century. Apple's valuation is huge, but analysts say that the fundamentals back it up. Despite its monumental rise, Apple's stock is still trading at just 14 times its expected earnings per share for 2012. That's relatively cheap, considering that the tech-heavy Nasdaq 100 trades at about 18 times future earnings. According to CNN Money, Apple had $127.8 billion in sales during the 2011 calendar year, putting it neck-and-neck with Hewlett-Packard (HPQ, Fortune 500), the nation's largest tech company by revenue. This year, Apple is on pace to become the biggest technology company in the world, measured by revenue, outpacing current global No. 1 Samsung. Last quarter, Apple posted $13 billion in sales. It was one of the most profitable quarters ever for any U.S. company, trailing only ExxonMobil's (XOM, Fortune 500) record-setting $14.8 billion quarter from the fall of 2008, when oil prices were at an all-time high
