HP chief financial officer Robert Wayman, who has been with the company 36 years, took over as interim CEO, while Patricia Dunn, an HP director since 1998, was named non-executive chairman of the board.

Fiorina, whose toughness and uncompromising character made her one of the most visible businesswomen in the United States, crafted HP's controversial, 20-billion-dollar purchase of computer maker Compaq in 2002.

"While I regret the board and I have differences about how to execute HP's strategy, I respect their decision," said Fiorina, whose differences with the board became increasingly evident in recent months.

"HP is a great company, and I wish all the people of HP much success in the future," she said in a statement.

The board was to begin searching for a permanent CEO immediately.

"Carly Fiorina came to HP to revitalize and reinvigorate the company," Dunn said.

"She had a strategic vision and put in place a plan that has given HP the capabilities to compete and win. We thank Carly for her significant leadership over the past six years as we look forward to accelerating execution of the company's strategy," she said in a statement.

Later, in a teleconference with reporters, Dunn said the board wanted to "accelerate the growth of the company and that requires a lot of hands on execution."

She said the board had been deliberating on the company's and CEO's performances "for quite some time."

"I would not say that the decision was sudden," Dunn added.

The new interim CEO, Wayman, said: "It's profitable growth in all our businesses that we are seeking here."

Fiorina, born in Texas in 1954, worked 20 years at AT and T and Lucent Technologies before joining HP in 1999, replacing Lew Platt as CEO. Fiorina, whose first name is short for Carleton, became chairwoman in 2000.

The merger with Compaq was designed to make HP a PC powerhouse capable of taking on industry giant Dell in a sector whose profit margins are slim.

But opponents criticized her for diluting the value of HP's printer and accessory business, which had been the firm's most lucrative enterprise by far.

More than 17,000 employees were laid off in the merger, which also led to the departure of Walter Hewlett, son of HP co-founder William Hewlett, from the company's board of directors.

In early December, Fiorina confided that the board had discussed several times splitting HP into several separate entitites.

Goldman Sachs analyst Laura Conigliaro said it was unlikely that Fiorina's removal would lead to a merger or a split up of the company.

"Our understanding is that Carly Fiorina stepping down as CEO comes from an operational and performance difference with HP's board rather than a strategic one," she said in a research note.

Another analyst, Steven Fortuna of Prudential Equity Group, said, "A change at the top does not address the strategic challenges posed by IBM and Dell regarding low margins in the PC business, gradual encroachment on the printer franchise, and maintenance-heavy services business."

"We do believe the change increases the odds of the company being broken up, though we are not big supporters of such a step," he said.

Investors appeared to welcome Fiorina's departure, as the firm's stock jumped nearly 11 percent in pre-opening trade Wednesday. HP stock was up 7.30 percent at 1558 GMT.

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