Personal library shelves are about to get a lot lighter. After 244 years, Encyclopedia Britannica is putting an end to its print editions.

Maybe you didn't think that they were still putting out bulky 32-volume sets of the iconic reference books. You're not alone. It's been largely downhill since sales peaked when it sold 120,000 printed sets in 1990. It only cranked out 12,000 sets in 2010, and nearly a third of those $1,500 sets have yet to be sold.

It was inevitable.

The Internet made the volumes obsolete. Who needs annual updates when free online resources are updated perpetually?

The World Wide Web isn't perfect. Anyone can edit a Wikipedia entry. There's no telling where a Google (Nasdaq: GOOG) link will take you. However, it's a small trade-off for having access to information as quickly as it takes a webpage to load.

Britannica will live on in digital form. The privately held company has actually been profitable in recent years, largely because 85% of its revenue now stems from the largely digital education market.

Consumers still should have seen this coming long before everyone flocked online. After all, sales peaked in 1990 and the Internet -- at the time -- consisted mostly of online services used by a sliver of tech buffs.

We can probably point to the PC as the first real nail in the coffin of Britannica's printed set. Microsoft's (Nasdaq: MSFT) Encarta offered an entire encyclopedia on disc at a fraction of the cost of World Book and Britannica publications.

However, Encarta was also no match for the Internet. Microsoft eventually shuttered Encarta -- even killing off the online edition three years ago.

Google and Wikipedia simply have labor advantages that Britannica and even the curated Encarta lack. Volunteers contribute to Wikipedia for free. Google has it even better, as advertisers are willing to bid up keywords to pay for leads on queries.

We also can't let Apple (Nasdaq: AAPL) escape the lineup. The 2007 arrival of the iPhone transformed smartphones from corporate mainstays into consumer gadgetry. Suddenly it was that much easier to find out who the country's third president was or to settle a dispute over who won the 1972 World Series.

Have you seen those iPhone 4S ads featuring Siri? The digital personal assistant is another print encyclopedia killer.

So congratulations, Microsoft, Google, Apple, and Wikipedia. You've killed the print edition of the Encyclopedia Britannica. Now which one of you can tell me where I can go to dispose of my ancient set?

Out of the pool
Microsoft may have played a part in Britannica's print demise, but it too is susceptible. Do you know the two words that Bill Gates doesn't want to hear? Stumped? A timely report has the answer. It's free, but only for a limited time, so check it out now.