Only a handful of Apple I computers exist. One is expected to fetch $300,000.

Steve Wozniak was giving it away free.

The Apple co-founder tweaked and soldered computer circuit boards in the mid-1970s from his cubicle at Hewlett-Packard and an apartment in Cupertino, California. He shared the design freely, showering enthusiasts in Silicon Valley's Homebrew Computer Club with gratis innovation.

The members were wowed by the intricacy and beauty of crisp lines and symmetry of Wozniak's handcrafted, meticulous design. One early club attendee, a local computer enthusiast, made note of the potential as talk of the board surged in the valley.

We'll come back to him shortly.

Steve Jobs saw the design - and the interest at the club - in July 1976, Wozniak told Bloomberg. That was three months after co-founding Apple with Wozniak. Why not sell the boards? The Byte Shop in Palo Alto agreed, but store owner Paul Terrell would only buy completed boards that did not need further tweaking at home.

Those computers became the Apple I.

Now more than 40 years later, one of about 60 surviving machines out of 200 made - and rarer still, fully functioning and untouched by modifications - will be auctioned on Sept. 24. It is expected to fetch upward of $300,000 next month.

"This computer tells a lot of about the history and genesis of the largest tech company in the world," Bobby Livingston, a spokesman for RR Auction, told The Washington Post on Monday.

Even the manual points to the scrappy, renegade early days of the company - it has handwritten notations from an Apple employee, Livingston said.

Since then, Apple has moved from Wozniak's cubicle and Jobs's garage to be the first company worth $1 trillion (yes, with a T). The Apple I, one of the first home personal computers, was modestly powered and ran very basic games and programs. It set the stage for the Apple II; its lower price point and accessibility completely changed how people interacted with computers.

A buyer paid $666.66 for this particular Apple I sometime between late 1976 and early 1977, the auction house said. But the buyer apparently wasn't as wowed as the club members.

The enthusiast, a co-worker of the buyer, got it secondhand about a year later. He paid $300 and learned programming languages to work the machine. He kept it ever since. An imprint on the board reads: "Apple Computer 1, Palo Alto, Ca. Copyright 1976."

RR Auction did not say who the man was, citing his privacy concerns. He tried selling it back to Wozniak for $10,000 in 1982, but the offer went unanswered, the auction house said.

The Apple I's condition is exceptional not just because of the computer's age, but the way users handled their machines. The boards were sold without cases, Apple I expert Corey Cohen said, and buyers typically made them at home. They soldered chips and sliced boards with razor blades to make modifications on the board.

But this machine is untouched in that way, Cohen told The Post. He evaluated the Apple I in June for the auction house. He fired up the system with a surplus keyboard the professor had originally used and hooked up a power transformer and vintage security monitor.

It boots up just as it would have all those years ago, Cohen said, and it ran with no issues for eight hours. He made minor restorations like cleaning some connections and carefully brushing away the remains of four decades worth of storage.

"The dust was not vintage 1977 dust," he said.

Cohen certified the machine with an 8.5 condition rating. That was estimated from the baseline 9.5 rating given to an Apple I computer that was preserved under glass just a few years after production, Cohen said. The Henry Ford Foundation acquired it for $905,000 in 2014.

There have been a recent auction run of Apple Is in recent years, but that does not indicate a glut, Cohen said.

About 60 are confirmed to exist on a registry, but only about 15 are still working, Cohen said. People who held on to them are getting old, and they are either selling them or leaving them in wills. In a few years, the circulation at auction will likely dry up, he said.

"Whoever purchases [this Apple I], it will not change hands again in our lifetime," he predicted. "They're either going to be in a museum or someone will not sell."

Perhaps the buyer can boot up software the way Cohen did in his test. The Apple I used audio tape to run software. But the tapes have the drawback of needing to be rewound.

He did not have to deal with that for his program, which depicted the Apple logo in stark monochrome along with an image of a young Jobs.

To do that, Cohen used audio from another Apple invention that changed the world - an iPod.