In a note to clients -- as reported by "AppleInsider" (www.appleinsider.com) -- Piper Jaffray analyst Gene Munster thinks the rumored "iPad mini" will have a cannibalization rate of 20%. In other words, every mini's sold would take the place of one full-size 9.7-inch iPad.

Assuming an iPad mini goes on sale Friday, Nov. 2 (Apple is expected to unveil it at an Oct. 23 media event), Munster forecasts Apple to sell at least five million units in the December quarter. That would be enough to cannibalize a million regular iPad units during the holiday shopping season, he says.

Previously, the analyst had forecast sales of 21 million iPads in the December quarter. However, with the expected launch of the iPad mini, he's increased his total iPad sales prediction to 25 million. For calendar year 2013, Munster's unit forecast has risen from 86.5 million to 95 million.