IBM is in talks to buy Sun Microsystems Inc for a proposed $6.5 billion cash offer, the Wall Street Journal reported Wednesday.

The merger, if completed, would mark a big consolidation step in the market for high-end server computers used in corporate data centers. The move may even prompt an antitrust challenge.

Together, the two companies would own about 65 percent of the market for server computers running the Unix operating system and 42 percent of the total server market.

Armonk, N.Y-based IBM is offering to pay at least $6.5 billion, or double Sun's Tuesday closing price of $4.97.

Shares of Sun jumped 60 percent in morning trading to $7.97, while IBM shares fell 2.15 percent to $90.91.

If the deal is successful, it will be IBM's largest-ever acquisition, and illustrate the company's intention to move from its recent strategy of focusing on deals to strengthening its software and services businesses, rather than hardware.

Acquiring Sun would help IBM accelerate its increasing adoption of open-source technology. Sun Microsystems created both the Solaris operating system, a version of Unix, and the Java Internet programming language. The two companies support the open-source Linux operating system, a rival to Microsoft’s Windows in data centers and on some desktop personal computers.

In January, Sun reported a loss of $209 million for the three months ended in December, weighed down by a $222 million restructuring charge.

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