By Kasper Jade and Katie Marsal

Published: 01:00 PM EST

Apple Computer in September plans to unveil a new line of iMac computers with faster processors and a little surprise to boot, AppleInsider has learned.

It will be the third time the Cupertino, Calif.-based company has introduced upgrades to its flagship, all-in-one consumer desktop line in less than twelve months.

Apple selects Merom

People familiar with the Mac maker's plans say it will sidestep Intel Corp's Core 2 Duo desktop processors, formerly code-named Conroe, in favor of adopting the mobile variant of chips, previously known as Merom, throughout the entire line. The company will also add a new member to the iMac family, a stunning 23-inch model, those same people say.

Apple's decision to forgo the use of Conroe in both its iMac and Mac Pro desktops suggests the chips are unlikely to find their way into the company's Mac computer line this year. It also explains why the Mac maker has yet to introduce new iMac models despite widespread availability of Conroe for several weeks. By contrast, Intel has only begun to ship Merom in production quantities within the last few days.

Conroe, the unpopular kid in class

While many Apple followers had initially projected Conroe to find a seat in the recently introduced Mac Pro high-end desktops, AppleInsider was first to report this past July that the company had selected Intel's higher-performance Xeon server processors instead.

Speculation immediately turned towards Conroe making an appearance in the iMac line, but insiders say Merom's lower power requirements and reduced heat dissipation are better suited for the iMac's sleek and ultra-compact industrial design.

Up to 40 percent speed increases

Still, preliminary tests indicate that Merom will offer up to a 40 percent speed increase over the Yonah chip it replaces -- the same chips found in the existing line of iMacs. Merom is available in speeds of 2.0GHz, 2.16GHz and 2.33GHz.

Third time's a charm

For Apple, September will mark the third time it has updated the iMac line in less than a year. Last October, it debut the iMac G5 with built-in iSight. Almost immediately, it followed up with the iMac Core Duo in January -- the first Mac to make the transition to Intel processors.