The earthquake shaking the personal computing business is ratcheting upward in intensity with a new report pointing out more clearly than ever that PC makers must find someway to exploit demand for tablets.

As No. 1 (or No. 2, depending on the source) PC manufacturer Lenovo rolls out a growing number of tablets, IDC on Wednesday increased its forecast for tablet sales beyond big numbers for this year to even bigger totals by 2016 with shipments set to more than double.

Even as another research firm, iSuppli, has predicted a decline in PC sales this year and IDC as well as Gartner are noting sluggish PC performance, the news is good for Apple and other firms that have embraced Android for tablets.

However, Apple’s tablet share is shrinking – news that helped send Apple shares down 6 percent Wednesday.

Microsoft, meanwhile, a late entrant into tablets with the Surface and its touch-sensitive Windows 8 as well as mobile focused Windows RT, is going to benefit from the seismic shift among consumers and businesses worldwide to go tablets.

IDC upped its 2012 tablet sales forecast to 122.3 million from 117.1 million, reflecting the launch of new iPads such as the Mini and the Surface.

Looking ahead, IDC forecast sales of 282.7 million by 2016, up from a previous estimate of 261.4 million.

Watch Out for Microsoft

By 2016, Apple’s iOS will still rule the market with a share of 49.7 percent with Android lagging behind at 39.7 percent. However, both shares are down from 53.8 for iOS and 42.7 for Android this year.

The reason? Microsoft. While some analysts have questioned the impact of the Surface and Windows 8 in general on PC sales, IDC researchers believe Microsoft has a winning program.

IDC says Microsoft will own a 10.3 share in tablet operating systems by 2016, up from 2.9 percent.

A rising tide for tablets also lifts the top three providers, however, as IDC forecasts strong annual growth rates of 20.9 percent for Apple, 21 percent for Android and a whopping 69.2 percent for Microsoft.

IDC describes the tablet market as a “strong competitive landscape” with companies in a constant battle for bigger or smaller, better and faster, and in some cases even lower priced devices.

“Tablets continue to captivate consumers, and as the market shifts toward smaller, more mobile screen sizes and lower prices points, we expect demand to accelerate in the fourth quarter and beyond,” said Tom Mainelli, research director for tablets at IDC, about the market trends. “Android tablets are gaining traction in the market thanks to solid products from Google, Amazon, Samsung, and others. And Apple’s November iPad mini launch, along with its surprise refresh of the full-sized iPad, positions the company well for a strong holiday season.”

IDC points to Lenovo as a”top-tier” company focusing on lower-cost Android tablets in their bids to battle the iPad phenomenon. However, Lenovo is hedging its bets with Microsoft, too.

Bad News for eReaders

However, the report  has bad news for ereader builders such as Amazon and Barnes and Noble.

“Once again, IDC’s increase in tablet shipments comes at the expense of eReaders. IDC once again lowered its forecast for ereaders for 2012 and beyond,” IDC said.

“While the front-lit ereader offerings from Amazon and Barnes & Noble have captured the interest of a subset of consumers who prefer a dedicated ereader, most buyers are gravitating toward multi-use tablet products and finding a ‘good enough’ reading experience on these traditional back-lit tablets. IDC now expects 2012 eReader shipments to top out at 19.9 million units, down from the 27.7 million units that shipped in 2011.”