A China Airlines Boeing 747. Bayne Stanley/Zuma Press/PA Images In a mining boom, buy the shovels.

It’s one of the oldest investing axioms, and anyone with shares in chipmakers AMD and Nvidia are reaping the rewards right now.

As the price of Bitcoin and Ethereum explodes, cryptocurrency miners are in a race to beat each other to the riches, and graphics processors are the tools they need.

They’re now in such short supply, one miner, Marco Streng, chief executive of Genesis Mining, made this extraordinary admission to Quartz:

"We are renting entire airplanes, Boeing 747s, to ship on time. Anything else, like shipping by sea, loses so much opportunity."

Entire airplanes.

That echoes the rush, sparked by Bitcoin’s price rise in late 2013, for $10,000 mining rigs that would now be on the scrapheap, worthless up against today’s machines.

But there’s a lot more at stake now. Ethereum, while trading at $240 compared to Bitcoin’s $3,400, is more readily available.

As much as 36,000 units a day can be mined ($8.6 million), and at one stage in June, the price hit $400.

But even as the price of Ethereum rises, the hardware and power supply costs remain relatively stable. So demand for processing units is soaring, and time, for miners, is money. Lots of money.

"You risk the opportunity to mine for the days you are delayed," Streng told Quartz. "If you are deploying 10 days later, you are losing 10 days of mining — that is the cost."

Both AMD and Nvidia feature as stocks millennials invest most heavily in on Robinhood, the app that lets you trade stocks without paying fees.

For AMD, the rush to mine Ethereum has provided an unexpected boon.

"Relative to cryptocurrency, we have seen some elevated demand," CEO Lisa Su said in the company’s earnings call following another beat last week.

"But it’s important to say we didn’t have cryptocurrency in our forecast, and we’re not looking at it as a long-term growth driver.

"But we’ll certainly continue to watch the developments around the blockchain technologies as they go forward."