An original Apple computer, hand-built by company founders Steve Jobs and Steve Wozniak 45 years ago, sold for $400,000 at auction in the United States on Tuesday.

The functioning Apple-1, the great-great-grandfather of today's sleek chrome-and-glass Macbooks, had been expected to fetch up to $600,000 when it went under the hammer in California.

The so-called "Chaffey College" Apple-1 is one of only 200 made by Jobs and Wozniak at the very start of the company's odyssey from garage start-up to megalith worth $2 trillion.

What makes it even rarer is the fact the computer is encased in koa wood -- a richly patinated wood native to Hawaii. Only a handful of the original 200 were made in this way.

Jobs and Wozniak mostly sold Apple-1s as component parts. One computer shop that took a delivery of around 50 units decided to encase some of them in wood, the auction house said.

"This is kind of the holy grail for vintage electronics and computer tech collectors," Apple-1 expert Corey Cohen told the Los Angeles Times ahead of the bidding. "That really makes it exciting for a lot of people."

John Moran Auctioneers said the device, which was sold with a 1986 Panasonic video monitor, has only ever had two owners.

"It was originally purchased by an electronics professor at Chaffey College in Rancho Cucamonga, California, who then sold it to his student in 1977," a listing on the auction house's website said.

The Los Angeles Times reported the student -- who has not been named -- paid just $650 for it at the time.

While the $400,000 hammer price represents a healthy return on investment for that former student, it is a long way short of the record for such a device.

A working Apple-1 that came to the market in 2014 was sold by Bonhams for more than $900,000.

"A lot of people just want to know what kind of a person collects Apple-1 computers and it's not just people in the tech industry," Cohen said.

Apple raced to success in the late 1970s and early 1980s, but foundered after the departure of Jobs and Wozniak.

The company was reinvigorated in the late 1990s, and Jobs was brought back into the fold as the chief executive.

He oversaw the launch of the iPod, and later the world-changing iPhone, before his death in 2011.