Question 1

Why is EVM storage so much more expensive than memory?

Accepted Answer

Storage is permanent — every byte you store must be maintained by every Ethereum node forever. This massive replication and persistence cost is reflected in gas prices. Memory, by contrast, exists only during a single transaction and is discarded afterward, making it dramatically cheaper.

Question 2

What is the difference between cold and warm storage access?

Accepted Answer

The first time you read or write a storage slot in a transaction, it's 'cold' — the EVM must fetch it from the global state trie (2,100 gas for reads, 20,000 for new writes). Subsequent accesses to the same slot are 'warm' (100 gas for reads, 5,000 for writes) because the data is already cached.

Question 3

When should I use memory instead of storage in Solidity?

Accepted Answer

Use memory for temporary data needed only during function execution: local computations, ABI encoding, intermediate results, and data you don't need to persist between calls. Use storage only for data that must survive between transactions: balances, approvals, contract configuration, and state that other transactions need to read.

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