Definition: Ethash

(ETHereum hASH) The mathematical puzzle used in Ethereum 1.0 to win the competition to place the next block on the blockchain. After Ethereum 2.0 proof-of-stake replaced Ethereum 1.0 proof-of-work, Ethash was rendered obsolete (see Ethereum 2.0).

RAM Intensive
Known as "ASIC resistant," Ethash was very memory intensive, which means that ordinary computers with a GPU had a greater chance of solving the puzzle than specialized ASIC hardware, which has less RAM.

Although Ethash took the header of a block and hashed it with a nonce (random number) similar to Bitcoin, an additional series of steps mixed the hash with random numbers generated from a large data structure created in RAM every 30,000 blocks. For the Bitcoin puzzle, see cryptographic hash function.