It is thought that a rare Apple I computer that may have been built by co-founder Steve Jobs may sell for more than $1 million at auction.

According to Apple historian Corey Cohen, there may only be 60-70 Apple I computers left in the world. Cohen is an Apple expert, and one of the only people who can tell an original Apple I from a replica, writes Don Reisinger for Fortune.

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Historic Apple I computer up for auction

Apple I computers have often been traded by enthusiasts who want to make applications for the old system, people who want to turn a profit on it, or own a slice of technological history. In contrast to the current high prices, they sold for surprisingly little in the 1990s, when Apple was struggling.

Prices were rising in line with the upturn in fortunes of the company, but spiked following Jobs’ death in 2011. In 2014 the Henry Ford Museum acquired an Apple I computer for $905,000, and the latest auction of the old computer could see prices rise even higher.

“That unit didn’t have the provenance that this board has,” says Cohen of the Apple I that The Henry Ford Museum bought. “This Apple I is a unicorn.”

Historian hails rare example of Apple computer

Cohen says that the model currently on sale is one of a handful of prototypes that were built in the early days of Apple, and has some different components from every other.

“This particular board looks like it was used as an experiment on memory and how much cheaper you could buy memory,” Cohen describes. “It was also used in experiments on getting ‘cleaner power’ to the memory chips.

The rarity of the computer makes it very attractive to potential buyers.

“There were some odd experiments on the board that someone like Steve Jobs or one of the Apple folks would have done,” Cohen adds. “It’s not something that would’ve been done by a hardware hacker back in the day.”

Kottke confirms age of device

The computer didn’t garner much interest outside of expert communities when it first came to market, however its price is skyrocketing. This particular Apple I belongs to an anonymous owner, who bought it for $18,000 in January 2000.

It is now up for sale on auction site CharityBuzz, and a portion of the profits will be donated to The Leukemia & Lymphoma Society. It seems to have been used to create a Spanish-learning program in a past life.

“CharityBuzz is thrilled to be auctioning the most unique and quite possibly the first Apple I computer in existence,” the company’s CEO Coppy Holzman tells Fortune.

The Apple I comes accompanied by a cassette, which contains the software that is required to run it. Cohen found some writing on the cassette, which he says could have been built by an old friend of Steve Jobs, Daniel Kottke, during the summer of 1976.

“The cassette tape included in the collection has Dan’s handwriting, which allowed us to date the cassette,” Cohen says. “Pretty much summer break 1976.”

Kottke since confirmed to CharityBuzz that it is his writing on the cassette. This means he is the man responsible for building the most valuable Apple I computer that exists.

Interestingly Jobs didn’t give any Apple stock to Kottke because he wasn’t an engineer. However co-founder Steve Wozniak did grant Kottke some shares.

“He’s the one who didn’t get Apple stock from Jobs because he didn’t want to give it to anyone who wasn’t officially an engineer, but Woz gave him stock,” Cohen says of Kottke.