Most blockchain virtual machines process transactions one at a time—like a single-threaded processor stuck in the 1990s. Solana's Sealevel runtime takes a radically different approach: it analyzes which accounts each transaction will touch, identifies non-conflicting operations, and executes them in parallel across all available CPU cores.
The result? Solana processes 50,000+ transactions per second while maintaining smart contract composability—something Ethereum's single-threaded EVM can't achieve even with L2 rollups.
Why Traditional Runtimes Are Slow
Ethereum's EVM executes transactions sequentially:
- Process transaction 1 → wait for completion
- Process transaction 2 → wait for completion
- Process transaction 3 → wait for completion
This design was chosen for safety: when every transaction runs in isolation, there's no risk of race conditions or state conflicts. But it's catastrophically inefficient. If you have 100 transactions that touch completely different accounts (Alice sending SOL to Bob, Carol minting an NFT, Dave swapping tokens), the EVM still processes them one by one—wasting 99% of your CPU cores.
Layer-2 rollups don't fundamentally solve this—they just move the sequential bottleneck off-chain.
How Sealevel Achieves Parallel Execution
Sealevel's breakthrough is explicit state dependency declaration. Every Solana transaction must declare upfront which accounts it will read from and write to. This isn't optional—it's enforced at the protocol level.
A typical transaction structure looks like this: