The Mountain View Computer History Museum is saying goodbye to one of its most unique exhibits, if not also its most priceless. However this computer might seem an awkward technological marvel — it doesn't run on electricity; it weighs upward of 5 tons, and its total memory is far short of a single kilobyte.

Nevertheless, the towering steel and brass contraption known as the Babbage Difference Engine for nearly eight years been one of the museum's main attractions. As designed by British engineer Charles Babbage in the 1840s, the Victorian-era machine works as a mechanical calculator that can determine polynomial functions. Today, his designs are hailed as the first working computer.

To be clear, the museum's difference engine isn't an original built 160 years ago by Babbage, but rather it is a working model painstakingly designed and assembled in the 1990s. Around the time when modern computers began garnering the world's attention, historians and computer buffs rediscovered the significance of Babbage's achievement as well as that his contemporary Ada Lovelace (considered the first computer programmer). To mark the 200-year anniversary of Babbage's birth, the Science Museum of London decided to build a working model of what is known as the Difference Engine No. 2, a design never built by Babbage that only existed in his plans and sketches. Fully constructing the machine took 17 years, about 8,000 custom-built parts and a seven-figure sum to complete.

The London Science Museum keeps one Babbage Engine on display, but its design team also assembled a second model for a private benefactor who financed the project. That donor, Nathan Myhrvold, a former Microsoft executive, originally loaned his Babbage Engine to the Mountain View Computer History Museum in 2008 with the idea to exhibit it for just six months.

Over the years, that deadline has been extended year after year, said Jim Somers, the museum's services manager. Over that time, museum officials estimate about 500,000 visitors have seen the machine and its regular demonstrations. But in recent months, Myhrvold informed the museum he wanted ship the machine to Seattle to put it on private display.

On Monday evening, a small crowd of the museum's employees held an after-hours party to swap stories and celebrate their last days with the machine.

"It's kind of sad for those of us who have seen it here for all these years," said Somers. "It's like a small child leaving the leaving the family. It's really been something special."

Sunday, Jan. 31, will be the last day to see the Babbage Difference Engine at the Computer History Museum, located at 1401 N. Shoreline Blvd. For museum hours and information, go to computerhistory.org.