The blockchain we know the most about is the original one, linked to Bitcoin. In a simple sense, this blockchain has been a resounding success. Since it began recording every Bitcoin transaction in 2009, the Bitcoin blockchain has more or less seamlessly kept the records of a currency that is now worth over $100 billion — and with no institution or person in charge.

But Bitcoin has so far failed at its goal of becoming a new kind of digital cash, which was the ambition described in the original documentation. So far, almost the only thing Bitcoin has been used for is a speculative commodity, like a digital gold, with lots of trading on the price. (The one place where Bitcoin has been used for regular real transactions is in the black markets.)

There are many reasons Bitcoin has not been more useful so far. The monetary policy and economics of Bitcoin — with only 21 million of the coins ever created — are a particularly fascinating question mark hanging over the project. As are the security issues that arise when every holder is responsible for keeping their own password, or private key.

But no problem has been more immediately stubborn than the limits on how many transactions the Bitcoin blockchain can handle. It turns out that when a whole bunch of people are keeping the records for something — as the blockchain design requires — there are limits on how many transactions all those computers can share and store in a set amount of time.

This issue — the so-called scaling problem — is now something that confronts essentially every major cryptocurrency out there. While Bitcoin can handle only around seven or so transactions each second, the second most valuable network, Ethereum, can do only double that, and none of them are getting close to the 50,000 a second that Visa manages.

Developers working on Bitcoin and Ethereum have been building several different solutions that might address this. Most of them involve adding new databases, with more capacity, on top of the ground level blockchain ledgers. So far, though, it’s not clear if these can work without introducing new problems or sacrificing the qualities that attracted followers to these projects in the first place.