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In this 1984 photo, Steve Jobs, chairman of Apple Computers, John Sculley, president and CEO, and Steve Wozniak, co-founder of Apple, unveil one of the earlier model Apple computers. (Sal Veder/Associated Press)

An auctioneer says one of Apple's first computers — a functioning 1976 model — has been sold for a record $668,000 US.

German auction house Breker said Saturday an Asian client, who asked not to be named, bought the so-called Apple 1, created by the tech company's founders, the late Steve Jobs and Steve Wozniak.

Breker claims it is one of only six known remaining functioning models in the world. Breker already sold one last year for more than $635,000.

It says the computer bears Wozniak's signature. An old business transaction letter from Jobs was also included.

The Apple 1, which was sold for $666 in 1976, consisted of only the circuit board, a case and a keyboard. A screen had to be bought separately.

Jobs and Wozniack assembled the first order of computers in the Jobs' family garage back in 1976.  Only 200 were built.

"It's really the holy grail of collectible technology," says Bob Luther, the author of The First Apple.