There's more than one way to make money from the Bitcoin craze, which has seen the value of the digital currency increase more than six-fold over the past few months. You can do it the old-fashioned way: buying low and selling high. But for the sophisticated digital-currency investor, there's a whole other world of Bitcoin speculation: the Bitcoin mining rig.

Like the currency itself, this strangely lucrative game is heating up – in a big way. One mining rig – available for preorder at a cost of about $1,800 in February – is now selling for more than $22,000 on eBay. And it hasn't even shipped yet.

Over the past year, a handful of companies have raced to build a new generation of computers that are specifically designed to mint digital money, and many speculators across the Bitcoin world are dying to get their hands on the latest hardware. This week, one of these companies, Butterfly Labs, is finally shipping its first custom-designed machines, six months behind schedule.

If Bitcoins are the fiat currency alternative for techno libertarians, then Bitcoin miners are the digital mint operators who keep the whole thing running. Bitcoin transactions are not registered with any central bank or brokerage firm or website. They're logged by a peer-to-peer network of computers. These computers keep track of who's transferring Bitcoins to whom, and then – every 10 minutes – they enter a kind of cryptographer's lottery, with the winner getting paid 25 Bitcoins for their work. That's how new Bitcoins get into the network. It's also how the Bitcoin miners earn their keep.

For Bitcoin miners, the name of the game is cryptography. And the lottery ticket is a hash – a number that represents a big bunch of data and is created via cryptographic algorithms. If one miner – or a group of miners – can take the transactions on the Bitcoin network and convert them into more cryptographic hashes faster than someone else, they have a better chance of winning that 25 Bitcoin payout. As Bitcoins have skyrocketed in value, the Bitcoin miners have been throwing more and more computing power onto the network.

When Bitcoins were first introduced, you could win the hashing lottery with a regular old personal computer. Now that's pretty much impossible. In fact, it now takes about 9 million times as much processing power to produce Bitcoins as it did in the beginning. So, for any Bitcoin miner to have a reasonable chance of winning, they have to seriously up their game.

That's where the new mining gear comes into play.

In the past year, three companies, Butterfly Labs, Avalon Asics, and Asicminer led a race to produce a new generation of computers built with custom-designed chips (they're called ASICS: application-specific integrated circuits) that do nothing but create tickets for the Bitcoin mining lottery.

You plug one of these machines into your computer, run special mining software, and sit back and wait for the Bitcoins. But they're so powerful that they're making things harder for other miners. "The difficulty has been skyrocketing lately as these ASICS have been coming online," says Gavin Andresen, chief scientist with the Bitcoin foundation.

Last summer, Bitcoin miner Scott Novich bet on Butterfly Labs. It seemed like a reasonable bet at the time because Butterfly had already shipped specialized Bitcoin mining rigs that, when pooled with other miners, were cranking out an average of four to six Bitcoins per month for Novich, a graduate student at Rice University. Butterfly had the best reputation; it had shipped well regarded mining rigs in the past. And its miners – which look like stretched out versions of the Roku media player – simply looked cool.

So last July, Novich and a few friends shelled out an advance payment of about $1,200 for a Butterfly miner that the company said would be able to perform more than 60 billion hashes per second. His current mining rig performs 750 million hashes per second.

The Butterfly gear was supposed to ship by November. Today Novich is still waiting.

The problem was that Butterfly – based out of Kansas City, Missouri – banked on a cool design and a brand new chip manufacturing process and ended up getting in over its head. "We've hit quite a few snags along the way, says Butterfly Chief Operations Officer Josh Zerlan.

The company had to redo its initial chip designs, but the worst snag was in November, when the Butterfly got a hold of its first chip samples. They were basically too hot to work, Zerlan says. "The plastic packaging on the top of the chip just couldn't exhaust the heat fast enough, so it basically melted the package."

Butterfly Labs )

And so, with customers growing angrier by the day, Butterfly was soundly beaten in the great Bitcoin mining race by Avalon Asics. Avalon used a less-cutting-edge chip manufacturing process, and it didn't pay too much attention to aesthetics, but it managed to ship out its first boxy, 67 Gigahash units back in February.

To hear CEO Yifu Guo tell it, Avalon won because they bet everything on a network of friends, college buddies, and acquaintances in China – who helped them build their first 300 systems in four months. After spending September and October last year working with "friends or people that were really smart" designing the systems, Guo flew to Shenzhen, China, where he spent another two months negotiating with the suppliers who would help him build his Bitcoin mining machines.

Guo called on his network to lend him cars, to introduce him to parts suppliers, even to ship packages. Avalon had sketched out the chip in the U.S., but it then paid (using Bitcoins, natch) a group of engineers at a Chinese computer company to build out the chip's design using specialized chip-making software that created specifications that the chip's manufacturer, Taiwan Semiconductor Manufacturing Company, could actually use.

"Nothing happens in Asia if you don't know somebody. It doesn't matter how much money you have," Guo says. "That's really what it came down to."

Those folks who've been lucky enough to get their hands on one of these early Avalon systems are cleaning up. Miner Jeff Garzik was the first person to take possession of a Avalon machine. Last year, he plunked down preorder money for a variety of custom ASIC rigs, including $1,300 for his Avalon system. "At the time, it was a very risky bet," he said in an email interview. "None of the ASIC vendors were shipping, and all were funding their efforts through a pre-order model, akin to Kickstarter. This meant any buyer was paying months in

advance for hardware that did not exist, and not even a guarantee of a refund upon failure."

But Garzik's Avalon bet paid off. Big time. He got his system the end of January. Within 20 hours, it had earned him nearly 15 Bitcoins. Today it cranks out just under 4 Bitcoins per day. That's about $500 at current Bitcoin exchange rates. "The first mover advantage is enormous," Garzik said in an email interview.

Avalon expects to ship another 1,200 rigs within the next month.

Until this week, Butterfly customers like Novich had been left on the sidelines, watching the compute power on the Bitcoin network rise up, day by day, while they waited.

Butterfly's Zerlan says the experience has been "very painful" and some customers are extremely angry. But reviewers and first-in-line customers are finally getting their hands on Butterfly's systems. Zerlan says that customers will still be able to make money mining Bitcoins. It will just take more time.

But with each new computer that ships, and each new adventurer that gets into Bitcoin mining, the bar is getting higher. Butterfly has already taken thousands of orders for the new systems. And Asicminer, which is both selling its own custom-designed machines and mining the Bitcoins itself, has already brought new custom ASIC systems to play.

So a year from now, the 750 megahash mining rig that Scott Novich is running at home may not be worth the power it sucks up. It really depends on how much a Bitcoin is worth in 2014. And that's anyone's guess.