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Ethereum Storage (or Storage) is a key/value store where keys and values are both 32 bytes. It is sparse (like a hash table), and there are no inherent gas savings from having two 32 byte values next to each other. Storing one of the values at key 1 and the other at key 1000, costs the same amount of gas as storing them at key 1 and key 2. (Gas savings from packing storage are still possible, such as fitting 2 uint128 values within a single key, instead of using 2 keys.)
See: Ethereum Memory
Source: https://ethereum.stackexchange.com/questions/1232/difference-between-memory-and-storage/1235