What makes the most valuable tech companies so valuable?

How do we value technology companies? Ingenuity and invention, quality of service, brand loyalty, manufacturing muscle, operating efficiency, supply-chain management, price, great place to work. There are lots of metrics.

For those unfamiliar with the wily ways of Wall Street, the stock market has its own way of expressing what it thinks of companies. It's called market capitalization or market cap for short.

Market cap is calculated by multiplying a company's share price by its total number of shares outstanding. There are other metrics for company fundamentals-- earnings per share, free cash flow, P/E or price-to-earnings ratio--but market cap has become an established indicator of market value.

I used market cap to determine the 10 most valuable technology companies. I stuck with electronics. If I hadn't, then Genentech would have replaced Qualcomm in the 10th spot. And since AT&T and other telecom companies are now just service providers--as opposed to the old days--they're out of the picture too.

So what makes these companies so valuable, at least to the market? Well, the obvious answer is their ability to consistently grow revenue and profits over time. On that, we can all agree.

Beyond that, however, there just doesn't seem to be much commonality. That came as a real surprise to me. I mean, wouldn't you expect to see a common thread or two, or at least a few with the same business model? I sure did.

Think about it. In the old days, the most valued companies were vertically integrated big-iron computer and telecom firms. They developed all their own software and hardware, they had their own research labs, they did everything. And they were all essentially similar.

Then came the personal computer and the industry disaggregated into companies specializing in chips (Intel), software (Microsoft), PCs (IBM, HP, Compaq, Dell), and networks (Cisco). Still, they were all part of the same industry.

Finally, we saw the rise of cell phones, consumer devices, and the Internet. That, I think, is when the industry really began to diversify. The dot-com bust and the dark years that followed just reshuffled the deck and brought Internet and network companies back down to earth.

Today, the top 10 list features a mix of products and services; hardware and software; enterprise and consumer; computers, communications and consumer electronics; network and Internet...there's some of everything.

And while these firms do have certain overlapping businesses, no two firms have the same business model, at least in terms of their primary revenue and profit-generating businesses.

I wonder, though, how long it will stay that way. Will the technology industry reaggregate? Is that even a word? Will there come a time when half the top valued technology companies are into robotics, virtual reality, or space exploration?

Your guess is as good as mine.