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Shaw Wu of Kaufman Brothers put out a research note Monday indicating that his latest run through Apple's supply-chain vendors indicates that new iMacs will be out sometime before March, or at most before June. It's been awhile since Apple tweaked the iMac in any substantial way, dating back to September 2007.

 

The changes this time around would mostly be under the hood: Wu believes Apple is debating whether to use Intel's dual-core processors or newer quad-core processors in the new iMacs. The dilemma is performance versus power consumption, as well as concerns that using quad-core chips in the iMac could steal business from the Mac Pro, currently the only system in Apple's lineup that uses quad-core processors.

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http://news.cnet.com/8301-13579_3-10149823-37.html?part=rss&subj=news&tag=2547-1_3-0-20

 More clues...

 AppleInsider reports that Apple has begun warning resellers that new orders for the high-end 24-inch iMac may not be filled due to decreasing supplies. Let's look at what we know about a possible iMac refresh. We'd heard rumblings before, but if true, this warning is a pretty clear indication of a refresh....

http://i.gizmodo.com/5143476/apple-warns-resellers-of-reduced-imac-availability-new-models-on-the-way