An Apple 1 motherboard thought to be one of only 50 in existence – and only six in working order – has sold at auction for just under US$375,000.

The price was more than twice the US$180,000 top estimate by auctioneer Sotheby's.

According to a BBC report, only around 200 of the 1970s-era motherboards were ever created. The identity of the buyer has not been revealed.

At the same auction, a memo written by Apple co-founder Steve Jobs sold for US$27,500. This was originally estimated to go as high as US$15,000.

The high prices shouldn't come as a big surprise, with Apple memorabilia traditionally doing well at auction. In December, the document establishing the Apple Computer Company signed by Jobs and his two other co-founders, Steve Wozniak and Ron Wayne, sold for US$1.35 million.