Solana and Ethereum are both programmable blockchains, but they were designed with different approaches to how transactions are processed. Ethereum is built around the Ethereum Virtual Machine (EVM), where developers deploy smart contracts that users interact with through transactions. Ethereum currently uses proof-of-stake, with validators staking ETH to participate in securing the network. 

Solana also uses proof-of-stake, but its architecture includes Proof of History (PoH) as a way of creating a verifiable record of time and ordering events. PoH is not a replacement for proof-of-stake; it works alongside Solana's consensus design. The idea is to give the network a cryptographically verifiable clock, helping validators establish the order of events without relying only on messages about when those events happened. 

So, the difference isn't simply that one uses proof-of-stake and the other doesn't. Both use PoS, but their underlying architectures and transaction-processing models are different.

Yet another important distinction relates to how the two systems manage application state and perform transactions. The Ethereum protocol employs accounts and smart contracts running in the EVM. A smart contract holds code and data and may be called by users and other contracts. Additionally, Ethereum is increasingly using Layer-2 networks like optimistic and zero-knowledge rollups to perform transactions off-chain while employing Ethereum for settlement and security purposes.

The Solana protocol works differently. It utilizes stateless programs which represent pieces of executable code, while mutable data is stored in accounts separately. A transaction indicates the accounts it needs to access. This approach enables Solana to recognize non-interfering transactions which it executes concurrently.

This is a significant architectural difference. Solana is built specifically for efficient execution on its main network, while the scaling architecture employed by Ethereum becomes increasingly based on Layer-2 networks that operate on top of Ethereum's base layer. Neither of them is automatically "better", as they make

Fees and the user experience is yet another clear distinction. For Solana, fees are paid in SOL and include both a base fee and a priority fee when necessary. The current Solana documentation mentions a base fee of 5,000 lamports per signature, while priority fees can be incurred when the user wishes for their transaction to be scheduled more quickly. 

For Ethereum, gas measures the amount of computation necessary for completing transactions on the network. Fees are paid in ETH, and the base fee is burnt with an optional priority fee paid to the validator.

Overall, however, Solana and Ethereum are much more than mere competing variants of the same blockchain. They represent fundamentally different architecture choices. Solana has chosen the tight integration and high-throughput path at the base layer level, while Ethereum built a multi-layered network architecture, where the mainnet is just one of several layers alongside rollups.