Shares of Sun Microsystems ( SUNW) thrilled to a rare pop today, jumping 8% on rumors the troubled server and storage maker might be acquired. But analysts threw cold water on the takeover story, while a trader said the strength likely stemmed from a massive institutional buy.

The stock rose 27 cents, to $3.61, in early afternoon trading, on heavy volume. Nearly 62 million shares already were changing hands, compared with average daily volume of 48 million, according to Baseline.

At UBS Warburg, Jack Francis, co-head of equity trading, said the sudden surge in price followed a 5-million-share block trade, considered to be a very large buy by Wall Street standards. "That was spurring stories of a potential takeover, which doesn't make any sense at all but did add fuel to the upside," said Francis. "The rumor doesn't hold a lot of weight, but in a market like this it gets people off the fence who are looking for any story that could generate alpha."

Further undercutting the acquisition theory, shares of both IBM ( IBM) and Dell ( DELL) -- both named as likely acquirers -- traded up Friday. Typically the stock of an acquiring company would trade down. H-P ( HPQ), viewed as a less likely acquirer since it's still digesting its purchase of Compaq, was also gaining slight ground.

IBM gained 93 cents, or 1.1%, to $86.82. Dell was up 40 cents, or 1.4%, to $29.58. H-P tacked on 10 cents, or 0.6%, to $16.60.

At Fulcrum Global Partners, analyst Robert Cihra said a purchase of struggling Sun by any of the three tech leaders wouldn't make much strategic sense anyway. "It would make no sense for Dell, which is focused on the sweet spot of the market, Intel-based servers. They would never want proprietary Unix platform, I wouldn't think." (Fulcrum doesn't do investment banking.)

"H-P already has two proprietary Unix lines , of their own plus Compaq. They certainly don't need a third. They need fewer, not more. And I doubt H-P's in a position to be buying another large company -- that seems suspect to me."

"That leaves IBM. But IBM is executing well against Sun using IBM's own products. I'm not sure why they'd feel compelled to own Sun's platform. That would just saddle them with competing Unix."

Sun's proprietary, high-margin product lines have struggled as corporate buyers have increasingly opted instead for standards-based hardware running on Windows and powered by Intel chips. In the first quarter of 2003, Sun was the only leading vendor to see a decline in worldwide server shipments, according to market research firm Gartner.

Sun saw shipments actually contract 13%, while rivals H-P, Dell, IBM, and Fujitsu all managed to grow shipments. Sun's share of the market also slipped from 6.3% to 4.9%.