Hard forks are incompatible changes to systems. Hard forks have caused more grief than probably anything else in the history of blockchains. Additional hard forks are being discussed now by the Ethereum and Ethereum Classic communities to deal with issues caused by the recent denial of service attack spam. Fortunately, there is nothing problematic about the proposed hard forks. I will describe an analogous technology and details of the Ethereum and Ethereum Classic systems to show why all is well.
People own various computing devices. People also run various versions and types of operating systems. The Java Virtual Machine (JVM) allows disparate systems to all run programs and get the exact same results. People have implemented the JVM in hardware, but, most just simulate it in software. Some use compilers with no optimizations. Some use "just in time" compilers. Some use "ahead of time" compilers. Few care about the differences in JVM realizations as long as program results are always identical. If a complex Java based weather simulation predicts the temperature in one week will be 78.91775159 °F, and all JVM instances also compute 78.91775159 °F, then everyone is happy.
The Ethereum and Ethereum Classic systems are also "virtual" machines. They are imaginary machines that are simulated. There is no Ethereum or Ethereum Classic world computer located in a bunker somewhere. The JVM allows everyone to effectively run programs on identical clones of a computer. Astonishingly, Ethereum and Ethereum Classic allow everyone to effectively run programs on the same instance of a computer. In other words, it is as if everyone is using the same single machine! As with the JVM, few care how this is done as long as the results are the same. The recent denial of service attacks took advantage of the way the systems are currently simulated. The proposed hard forks will just improve the efficiency. All results will remain the same.
The state of the Ethereum and Ethereum Classic systems at all times depends on all the previous activity. Computations affect accounts. There are external accounts and contract accounts. All accounts have four components: an ether balance, contract code, storage dictonary (associative array), and, a counter (nonce). For external accounts, the counter tracks the submitted transactions. For contract accounts, the counter tracks the created contracts. There is no reason for network nodes to store anything for accounts that either do not exist or are empty. The attacks created millions of empty accounts that are using massive amounts of storage. The proposed hard forks will just stop wasting space for these accounts.¹ As this storage is not in the blockchain, no changes to the blockchain are involved.
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I would like to thank Elaine Ou, Nick Johnson and Smokyish for their help. I would also like to thank IOHK (Input Output Hong Kong) for funding this effort.
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<3for the original Ethereum vision