In buying Rational Software, IBM again plugs a gap that remains at its competitor.

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Last year IBM bought Borland competitor Rational Software , but Fuller thinks customers still want a tools company that isn't controlled by a giant.

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Earlier in his career, he founded Pure Atria Software, where he was CEO until the company was acquired by Rational Software Corporation in 1997.

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"It's not like Big Blue is watching you, " says Rebecca Swanick, a marketing director at IBM's Rational software division, who uses the technology at trade shows.

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In particular, he mentioned Rational Software's Windows-compatible file system ClearCase.

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Its Rational Suite of software and information management software continued to suffer due to low demand and transactional rollover into the next quarter.

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When the acquisition closes in the first quarter, Rational will be the fifth division within IBM software, along with Websphere, DB2 database, Tivoli management products and Lotus collaborative software.

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Rational also gives IBM greater means to drive its pervasive computing goals--that is, specialized software for specific devices.

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