The following commentary comes from an independent investor or market observer as part of TheStreet's guest contributor program, which is separate from the company's news coverage.

NEW YORK (

Trefis

) --

Apple

(AAPL) - Get Report

is continuing to perform well in a rather slow-growing global PC market.

The U.S. PC market declined for the first time in the decade last year, hurt by soft economy, supply shortages and the popularity of smartphones and tablets. According to a report, the major PC players such as

Hewlett-Packard

(HPQ) - Get Report

,

Dell

(DELL) - Get Report

and Acer all saw declines in their U.S. sales while Apple was the standout performer.

Apple saw 21% growth in Mac sales in the U.S. market compared to the year ago quarter, pushing past Toshiba and Acer to take the No. position behind HP and Dell.

Last week, Apple unveiled the new Mac operating system, OS X Mountain Lion, which has over 100 new features. It is through these innovative efforts that Apple has managed to consistently beat the overall PC market growth for 23 straight quarters.

Apple's Mac accounts for about 12% of

our $550 price estimate for Apple stock. Our price estimate is about 10% above the current market price.

See our complete analysis of Apple

here.

With the new OS, Apple will come out with updates to its messaging service, notifications app, gaming center, sharing features and integration with the company's online service, iCloud. The new Mac software will also support a feature called AirPlay Mirroring that allows users to stream music, videos or photos on their iPhone or iPad screens to their HDTV via Apple TV. These features should help Apple continue to gain share in the PC market.

We estimate that Apple's share in the notebook segment has increased from 4.8% in 2010 to 6.2% in 2011. If this trend continues, Apple could easily beat our estimates for market share growth in the coming years.

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This commentary comes from an independent investor or market observer as part of TheStreet guest contributor program. The views expressed are those of the author and do not necessarily represent the views of TheStreet or its management.