IBM’s Building 25 – the focus of preservation lawsuits and a planned big-box retailer – was destroyed in a Saturday fire, leaving a charred husk of a structure preservationists had hailed as the precursor to modern high-tech campuses and where the forerunner to the hard drive was invented.

Saturday’s blaze came while preservationists and Lowe’s, the home improvement store, were cobbling a settlement that would have ended the years-long legal battle over the structure. An imminent deal would have allowed both the mega-store and a portion of the historic building to share the Cottle Road site.

Saturday’s blaze unnerved preservationists because it was the latest in a string of San Jose historic buildings that burned in a year.

“This is devastating, in every sense of the word,” said Brian Grayson, interim executive director the Preservation Action Council of San Jose, which had sued to protect the building. “We are obviously very concerned at the recent losses of a number of the city’s historic buildings by fire.”

Despite recent controversies, Building 25 was “an important building,” said Patricia Colombe, vice chair of the city’s Historic Landmarks Commission. “A lot of people haven’t felt warm and fuzzy about it because it was a modern building.”

In 1957, architect John Bolles – who designed Candlestick Park – created a then-fresh workplace for IBM. Unlike the dark old economy factories, Advanced Research Building 25 had a long spine with eight wings jutting out, four on each side.

Floor-to-ceiling windows brought in sunlight, blurring the connection between indoors and out. A horseshoe pit sat outside, available for afternoon distractions. Such concepts would be repeated in later high-tech campuses with their outdoor courtyards and game rooms.

It was here IBM researchers invented the flying head disk drive, which allowed real-time on-line transactions such as airline reservations. When Communist Party Secretary Nikita Khrushchev visited the United States in 1959, his hosts brought him to Building 25.

Not everyone agrees the building is historically important. The company left the building in 1996, said spokeswoman Colleen Haikes. Over the years, it erected a chainlink fence after vandals broke in. Homeless people reportedly camped there.

“IBM’s intent is to sell that site because it’s been unoccupied and we don’t have a purpose for the building,” she said.

In November, Mayor Chuck Reed said, “This particular building is not one of great merit.”

The city had sided with Lowe’s wishes to raze the building and make room for a 180,000-square foot store which would send an estimated $500,000 annually in sales tax to city coffers. However, lawsuits delayed the plans; preservationists had argued that the city hadn’t properly considered whether Lowe’s could successfully build a smaller store and still accommodate Building 25’s conservation.

That opportunity seemed lost when the fire hit at 1:32 a.m. Saturday.

“There’s no remodeling that,” fire Capt. Dave Parker as he glanced at the smoldering building. The brick anchors remained but the windows were gone, as were most of the exterior upper tiles designed to resemble an IBM punch card.

Saturday’s fire was the latest in a series of blazes that have claimed historic buildings this past year.

A suspicious January fire burned the Porter Stock Building on South First. And last July, the old Victorian-style home of Eliza Donner Houghton, a survivor of the ill-fated Donner Party, burned in another suspicious blaze.

To that list, historian Franklin Maggi would add the Fifth Street home that was the site of a fatal fire in November; it was once the bungalow of a Japanese-American midwife and many Nisei were born there. And though it might not be on historic registers, Maggi included a 1870s shotgun-style building in River Street historic district lost to flames last fall.

Colombe said the commission may consider ways to protect such buildings.

“That might be a question for the future,” she said. “Is there something cities in general can do to provide better protection for historic buildings that are vacant. Vacant is key, because vacant buildings do burn sometimes.”

However, she noted having so many burn in a year was unusual. And she lamented the latest loss.

Saturday’s fire was so extensive, that firefighters worked eight hours before controlling the flames at the sprawling building. They were still at work Saturday afternoon, dousing potential hot spots to prevent any flare-ups while curious pedestrians from the nearby senior center strolled by get a closer look at the much-discussed building.

No cause has been determined, said Capt. Anthony Pianto. The area is being treated similar to a crime scene, which is common with undetermined fires.

City officials have asked firefighters to take care with the building, said Battalion Chief Susan Salinger, in case anything can be salvaged.

Preservationists were confident a portion of the Building 25 would be reconstructed under the pending settlement, said the group’s attorney Susan Brandt-Hawley, who said had she consulted with Lowe’s attorney since the fire. Lowe’s did not return calls from the Mercury News on Saturday.

It’s better than nothing, said historian Maggi, who came to photograph the ruin Saturday.

“I’m very appreciative of early modern architecture in Silicon Valley,” he said. “And this represents the important growth of this period. It tells the development of Silicon Valley, which is important beyond just us.”