ARMONK, New York ( TheStreet) -- IBM's ( IBM) market capitalization has surpassed Microsoft's ( MSFT) for the first time in 15 years, marking the latest chapter in the hardware and software giant's recent growth.

IBM has been enjoying strong demand for its software and services, helping the tech bellwether put out consistently robust quarterly numbers. The company also raised its 2011 earnings guidance last month.

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Big Blue had a market cap of $205.2 billion at the close of play on Monday, compared to Microsoft's $203.82 billion.

Perceived on the Street as a solid and steady stock rather than sexy or hot, IBM has seen its shares gain almost 15% this year. Shares of Microsoft, however, are down more than 13% over the same period.

The number one software maker nonetheless beat analysts' third-quarter estimates last month, boosted by Kinect sales and a healthy corporate IT environment.

IBM shares closed down $1.90, or 1.12%, at $168.26 on Monday. Microsoft shares also headed southward, losing 32 cents, or 1.31%, to reach $24.17.

-- Written by James Rogers in New York.

>To follow the writer on Twitter, go to http://twitter.com/jamesjrogers.

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