Its market cap makes it more valuable than General Motors, Ford, General Electric (NYSE: GE), and AT&T combined. It's a company "estimated to be worth as much as the entire country of Spain." Its staggering valuation, built on the kind of profit margins those pre-computing dinosaurs could only dream of, grows and grows with each passing month as the company's stock price goes parabolic, and its proponents trip over each other to offer ever more outlandish price targets.

No, it's not Apple (Nasdaq: AAPL). The company I'm describing is -- or rather, was -- Microsoft (Nasdaq: MSFT), back in the days of dot-com yore. Microsoft began 1998 worth just over $150 billion and ended the millennium with a bang, worth $600 billion. I thought about that historical comparison when Bloomberg's daily chart showed that Apple was about to become more valuable than every publicly traded company in Spain, Greece, and Portugal combined. It's an incredible comparison, and one that's at least fairer than many of the outlandish Apple-to-oranges matchups found on the "Things Apple Is Worth More Than" blog. For those of you interested in keeping score, here are a few other things Apple is worth more than at the moment:

  • The construction of the U.S. interstate highway system.
  • All U.S. retail electricity sales.
  • One year's worth of global lottery sales.
  • Two Apollo space programs.
  • The entire U.S. Navy carrier fleet.
  • The entire U.S. retail sector.

With a newly instituted dividend and near-unanimity in bullish sentiment, it seems likely that Apple's market capitalization will soon surpass other ridiculously expensive milestones. But how far can it go, and how long can it remain ahead of the pack? The New York Times took a look back at the market's past market-cap rulers after Apple surpassed Exxon Mobil (NYSE: XOM) last year. There weren't a whole lot of companies to get to the top of the mountain -- just 10, not counting Apple. Some ruled for decades, but in recent years the crown's changed hands rather frequently.

Microsoft and Cisco each had their turn at the height of the dot-com boom, only to relinquish the throne to ExxonMobil as oil costs skyrocketed and energy again became a dominant economic theme in the mid-aughts. There's also something to be said for bubbly valuations coming back to Earth.

Looking back further, GE was the last company with significant manufacturing operations atop the market, holding the "world's largest" moniker through the mid-'90s. Before that, Wal-Mart and Altria, the former Philip Morris tobacco-led conglomerate, each briefly ruled. The last company to hold the crown for any extended length of time was IBM (NYSE: IBM), which lost its lead in the early '90s after a quarter-century at or near the top of the market-cap standings.

The companies that claimed the crown for any extended length of time did so behind fundamental transformations to modern life. AT&T and GM, two of the Times' earliest leaders, connected America in different but equally important ways, though GM wound up ahead for a longer period. Exxon (before the Mobil merger) rode the interstate highway system and the postwar economic boom to market-cap leadership before IBM started the long process of computerized automation that continues to change modern life with each passing year.

Once the '90s hit, the market seemed unable to decide which company was really driving the modern economy. Was it the big-box retailer, the energy-focused conglomerate, the operating-system monopolist, or the oil titan? For now, at least, the answer seems to be a mobile-device manufacturer, which is a rather radical shift. Retailing is all about efficiency, and oil is just a commodity. Apple's sales today have earned it its place in history, but the consumer-electronics industry has never suffered its kings to rule for long.