Sotheby's will put some Apple history on the block next month, including one of only six working Apple-1 personal computers. The auction house has estimated the motherboard will sell for up to $180,000.

Also up for sale: A memo written by former Apple CEO Steve Jobs during his time at video game maker Atari.

The Apple-1 -- which consisted of a circuit board hand-built by Apple co-founder Steve Wozniak -- first went on sale in July 1976 for $666.66. About 200 units were produced. According to the Sotheby's catalog listing (download PDF), there are about 50 surviving Apple-1 computers, but just six known to be in working condition.

"That's probably a pretty good estimate of original Apple-1s that have been operated in the last four or five years," said Mike Willegal, an engineer with a major technology company who has identified and indexed 41 Apple-1 computers. "If a unit hasn't been powered up in more than five or 10 years, it probably shouldn't be counted as currently working. These old computers tend to fail over time, even if they are just sitting on a shelf."

Unlike later personal computers, including the 1977 Apple II, the Apple-1 was sold as a fully-assembled circuit board, but minus a case, power supply, keyboard or monitor. Buyers had to provide those components, resulting in some interesting custom computers, several boasting handcrafted wooden cases.

Sotheby's estimated that the motherboard will sell for between $120,000 and $180,000 when it goes for auction. The lot also includes a cassette interface -- cassette tapes were used to store programs and data -- and several manuals, including a rare BASIC user's manual.

In late 2010, rival auctioneer Christie's sold an Apple-1 computer for just over $213,000, a record for the decades-old technology. But that Apple-1, while sporting some non-original parts, also included a letter signed by Steve Jobs.

That may make all the difference in the sales price of Sotheby's Apple-1, said Willegal.

"This unit works, and is fairly complete with documentation and original cassette interface, so it should draw a pretty good sum," said Willegal in a Sunday email. "[But] it doesn't have a receipt with Jobs signature, so I don't see it reaching the Christie's number."

Also slated for the June auction is a four-page memo on game design written by Jobs when he worked for Atari in 1974.

The memo, which includes a one-page addendum hand-written by Jobs, "was meant to improve the functionality and fun of World Cup, a coin arcade game with four simple buttons and an evolution from Atari's Pong game," according to Sotheby's (download PDF). It features three original circuit diagrams that Jobs drew in pencil.

Sotheby's put an estimate of between $10,000 and $15,000 on the report.

Last year, Sotheby's sold the original three-page contract that founded Apple -- signed by Wozniak, Jobs and the lesser-known Ron Wayne -- for nearly $1.6 million. The contract had been expected to sell for no more than $150,000.

That piece of Apple memorabilia was bought by Eduardo Cisneros, CEO of Cisneros Corp., a Miami company, and a director on the board of the south Florida-based Gibraltar Private Bank & Trust.

Bidding on the Apple-1 and Jobs' memo will take place in New York on June 15, starting at 10 a.m. ET.

One of just six working Apple-1 computers -- this circuit board -- will go on sale at Sotheby's next month, and may sell for as much as $180,000. (Image: Sotheby's.)

Gregg Keizer covers Microsoft, security issues, Apple, Web browsers and general technology breaking news for Computerworld. Follow Gregg on Twitter at @gkeizer, on Google+ or subscribe to Gregg's RSS feed . His email address is gkeizer@computerworld.com.

See more by Gregg Keizer on Computerworld.com.