In January 1975, Popular Electronics ran a cover story about a new computer for hobbyists. The Altair 8800 came as a kit and cost $439 (the equivalent of $1,778.58 in today’s dollars). It came with no on-board memory. You programmed it by entering Intel 8080 opcodes by hand via a series of switches on the front panel. Buying 4k of memory, the ability to read in programs from paper tape, and a teletype interface would increase the price 6 fold. You had to solder the thing together by hand. By comparison with the big university and corporate mainframes it was basically useless.

But Popular Electronics was the Make Magazine of its day and engineering schools had begun to require their graduates to learn some programming, so Forest Mims and Ed Roberts, the two guys in Albuquerque who’d put the Altair together, figured they could probably sell a few hundred in the first year to this emerging group of hackers avant la lettre.

They took 1,000 orders in the first month. Six months after the release they’d sold 5,000. By October of that year their company had 90 employees.

Why was the Altair such a runaway success? After all, by comparison to the cutting edge computers of its day, it was underpowered and extremely difficult to work with. The answer is ownership. The Altair offered bourgeoning hackers their first chance at a computer that would be fully and completely theirs. They could take it home, throw it up on their work bench, take it apart, put it back together and try to get it to do totally new unimagined things. They could program their Altairs to play Fool on the Hill through a transistor radio. They could build a board to let the Altair drive a color TV in Times Square. They could start a small company to sell programming languages for it. They could get together with their fellow Altair owners to share programs and cool hacks.

This last point can’t be emphasized enough. The Altair crystallized growing local groups of DIY computer enthusiasts like the Homebrew Computer Club in Silicon Valley. It gave them an outlet for their energies and an example of what could be done. It made them believe that their incredible fantasy of having their own computers might really come true.

And after that, there was no stopping them. This new generation of hackers dedicated itself with an almost religious zeal to spreading the idea of computer ownership across the world. They invented the personal computer — a whole industry dedicated to the notion that computers could make life better and work easier for everyone, not just huge institutions. The Homebrew Computer club alone included the founders of Apple, Ozborne (builders of the first portable), and a raft of other industry pioneers.

Today, the world of physical computing closely resembles the personal computer industry circa 1975. We’ve been around for a few years struggling around the edges with tools and products that were designed, priced, and packaged for serious industry, but we haven’t made any money and we haven’t moved the world. That’s about to change.

Recently, our Altair arrived. It’s called the Arduino. This is 2009 so instead of being built by two engineers in Albuquerque, it was built by an open source international cabal of programmers and professors.

A lot of people complain that it’s underpowered and overpriced (even though it only costs $8.64 in 1975 dollars). But you don’t need special hardware to program it. It lets you do all the basic tasks with just a line or two of perfectly comprehensible code. And there’s a thriving community of people busily using it to do all the useless, fun, creative things they’d always dreamed of if only they could get their hands on a computer that could sense and control the world around it. They’re using it to teach houseplants to call for help if they need watering. And they’re using it to play music on glasses of water.

If the Arduino is the Altair of physical computing then what will be its VisiCalc? What will be the killer application that makes the physical computer of the future a necessity for business. If the Arduino is the Altair, what will physical computing’s Mac look like? I don’t think anyone today knows the answers to these questions.

But the answers are coming. In the next few years, physical computing has as much of a shot at changing the world as technologies ever get. And this is the time to get involved. Unlike the web, personal computer, and green energy industries, physical computing is a space where two guys in a garage can come along and invent something that will touch billions of people around the world without anyone else’s permission. That’s because what’s needed in physical computing is not advanced research, massive infrastructure investment, or huge production facilities. What’s needed is close attention to applying the existing technology to solving human-scale problems. Microcontrollers and sensors, CNC milling machines and laser cutters, GPS devices and accelerometers need to be transformed into tools that regular people can use to improve their daily lives: to make themselves more connected to the people and places around them, to entertain, educate, and distract them.

In 30 years, when people tell the story of the Physical Computing Revolution and how it changed the world, what will they say about you?