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 ( ), 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 . "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.