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A key person behind the "$100 laptop" for schoolchildren has left the project as the organization overhauls its operations and prepares to tweak its open-source approach by welcoming Microsoft Corp.'s Windows.

While the One Laptop Per Child Foundation is known as the brainchild of the Massachusetts Institute of Technology's Nicholas Negroponte, his longtime MIT colleague Walter Bender was a close No. 2.

Bender oversaw software and content for the green-and-white "XO" laptops, whose user interface was specially designed as an educational tool.

But in March, after OLPC's initial run of its $188 laptops reached fewer children than originally envisioned, Bender became head of "deployment."

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Officially, OLPC said it was streamlining its organization because the laptop's technology essentially had been built.

A different view came from the XO's former top security architect, Ivan Krstic, who wrote on his blog that Bender got demoted.

Krstic said OLPC was undergoing a "drastic internal restructuring" and "a radical change in its goals and vision."

Then last week, Bender left the group entirely. That marked a third high-profile departure from OLPC.

In addition to Krstic, Mary Lou Jepsen, who had been chief technology officer, left in December.

Negroponte said Bender was burned out after helping to shape OLPC for two years, during which time it has sold more than 500,000 laptops for children in such countries as Haiti, Afghanistan, Rwanda, Peru, Uruguay and Mongolia.

But Bender already has new plans: to launch an independent effort to further the development of the XOs' homegrown software, known as Sugar, and get it to run on Linux computers other than XOs.

"Sugar is in a narrow place and it is ripe to be unleashed," he wrote in an e-mail exchange.

Sugar relies heavily on icons and other graphical features and avoids Windows' files-and-folders format.

That was done to be intuitive to children in developing countries who have never encountered a PC, but some governments have hesitated to invest in laptops without Windows.

Some competing low-cost laptops being billed as educational tools, such as the Classmate PC developed by Intel Corp., do run Windows.

For about a year, however, Microsoft has been working to get a slimmed-down version of Windows to run on XO laptops.

As a result, Negroponte said Tuesday that he expects XOs to soon have a "dual-boot" option, meaning users would be able to run Windows or Sugar.

One current hang-up is whether the necessary hardware would add $7 to $12 to an XO's cost, taking the project even further away from its eventual goal of producing the machines for less than $100.

Eventually, Negroponte added, Windows might be the sole operating system, and Sugar would be educational software running on top of it.

That might disappoint advocates of open-source software who helped bankroll OLPC and cheered the challenge it represented to Microsoft's dominance.

Unlike proprietary software like Windows, open-source applications are developed by a community of programmers and the underlying code is freely shared.

Wayan Vota, whose OLPC News blog reported Bender's departure Monday, said he feared Sugar would get neglected on XOs that run Windows.

"Which do you think Microsoft is going to put its marketing muscle behind?" he said.

Negroponte said he was mainly concerned with putting as many laptops as possible in children's hands.

He lamented that an overriding insistence on open-source had hampered the XOs, saying Sugar "grew amorphously" and "didn't have a software architect who did it in a crisp way."

For instance, the laptops do not support Flash animation, widely used on the Web.

"There are several examples like that, that we have to address without worrying about the fundamentalism in some of the open-source community," he said. "One can be an open-source advocate without being an open-source fundamentalist."

Besides rethinking the laptop's technology, Negroponte wants to get OLPC moving more efficiently. An executive-search firm has been looking for a chief executive for the group for more than a year.