Is this another tech bubble bursting?

That’s the stock market tumbling, led by a collapse in tech stocks: The overall market is down 18 percent this year, and tech shares are down about 30 percent.That sound is also a chorus of “I told you so” from people who’ve been comparing the bull market investors have enjoyed for many years to the dot-com bubble of the late 1990s — and who say things are going to get worse. The main one: Unlike the dot-com era, many of the most valuable publicly traded tech companies today are actual companies — they make and sell things people value, and usually make a profit doing so. So even if your only exposure to the stock market is via your 401(k) or IRA, you’re probably exposed to tech stocks.One way to measure the relative riskiness of a stock is by measuring its ratio of price to earnings (P/E) — how much does a share of a company cost compared to its profit?