SAN FRANCISCO (Reuters) - Sun Microsystems Inc <JAVA.O>, the world's fourth-largest server-computer maker, said on Thursday quarterly profit doubled, sending the shares up.

Net income rose to $260 million, or 31 cents per share, for Sun's fiscal 2008 second quarter ended December 30, from $133 million, or 15 cents per share, a year earlier. Revenue increased 1.4 percent to $3.62 billion from $3.57 billion.

The company's gross profit margin increased 3.5 percentage points to 48.5 percent. Sun recorded $32 million of restructuring charges in the period.

Sun said last week it expected to report second-quarter earnings of $230 million to $265 million, or 28 cents per share to 32 cents per share. It said revenue was about $3.6 billion, an increase of about 1 percent over the year-earlier amount.

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Its shares, down 18 percent this year through Wednesday, added 1.1 percent in extended trading following the earnings report after closing up 8.8 percent at $16.12 on Nasdaq.

Sun, based in Santa Clara, California, has been trying a comeback under Chief Executive Jonathan Schwartz, cutting jobs, selling server computers with processors from Advanced Micro Devices Inc <AMD.N> and Intel Corp <INTC.O> in addition to its own chips and growing in software.

Last week, Sun said it would buy Swedish database-software maker MySQL AB for about $1 billion to drive growth in its software services business.

Schwartz said in a statement Thursday the second-quarter results "highlight the demand set to fuel growth in the back half of the fiscal year."

The company had double-digit percentage growth in emerging markets including India, China, Latin America, Eastern Europe and the Middle East during the second quarter.

It also signed an agreement for Dell Inc <DELL.O>, the world's second-largest personal-computer maker, to sell computers with Sun's Solaris operating system.

(Reporting by Philipp Gollner; Editing by Jeffrey Benkoe)