I came across the term memory-hard while ready about ETH POW algorithm. What does it mean when someone says that POW is memory hard?
"Memory Hard" implies that amount of memory required to mine Ether with POW is significantly higher as compared to other implementations (such as Bitcoin).
This makes mining difficult since latency introduced by DAG lookups slows down mining.
This article explains the issue :
Ethereum uses Dagger-Hashimoto algorithm for POW.
miners use DAG dataset refreshed for each 30,000 blocks and mining process includes strict memory hard hashing functions
because of memory hard hashing functions, GPU and hardware specialized in Bitcoin mining are not faster than general CPU.