Introducing about dual-VM architecture of Polkadot Hub

Language: English

Author: Dustin

Level: Beginner

1. What is Polkadot Hub?

Polkadot Hub is a Layer 1 system chain within the Polkadot Cloud ecosystem that enables smart contract deployment and execution. It serves as the central hub for asset management, cross-chain communication, and decentralized finance applications. It combines Ethereum compatibility with native Polkadot innovations to create a unified platform for building scalable, interoperable DeFi applications.

2. The Multi-VM Trend

Given the current demand for computationally intensive applications—such as those involving privacy, ZK, and AI—and the trend towards developing diverse use cases, multi-VM support on a blockchain has become a necessity.

Here are some typical examples:

### Polkadot Hub

• It features a dual-VM architecture with two virtual machines: a PolkaVM (RISC-V) for native Polkadot logic and an REVM for Ethereum compatibility.
• This dual-VM approach allows developers to deploy smart contracts using either Polkadot's native environment or Solidity, enhancing scalability, interoperability, and performance.

### Arbitrum

• Arbitrum’s Stylus upgrade introduced a multi-VM environment, running the standard EVM alongside a WASM VM.
• This gives developers language flexibility (Rust, C++) and leverages WASM's strengths for high-performance logic, advanced DeFi, and on-chain gaming.

### Avalanche

• Supports three primary VMs: Coreth (C-Chain) which is EVM-compatible, Platform VM (P-Chain) for staking and L1 operations, and Avalanche VM (X-Chain) for native token operations.
• Developers can also create custom VMs using any programming language with familiar tools.

3. The Two Virtual Machines on Polkadot Hub

3.1 PolkaVM

PolkaVM is Polkadot's modern, next-generation execution environment built on the RISC-V architecture.

• Faster execution: Designed to be orders of magnitude faster than traditional EVM environments.
• Lower costs: Contracts run cheaper due to more efficient resource usage.
• Better performance: Uses a register-based design (like modern computer chips) instead of older stack-based systems.
• Future-proof: Optimized for advanced features like zero-knowledge proofs.

3.2 EVM/REVM

The second environment is EVM compatibility, delivered through REVM. Think of this as a bridge to the existing Ethereum ecosystem.

• Existing apps work unchanged: Developers can deploy unmodified Solidity contracts directly to Polkadot Hub.
• No rewriting needed: Developers don't need to change their code or tools—everything they know from Ethereum works the same way.
• Rapid adoption: Existing Ethereum projects can migrate with minimal effort.

3.3 PolkaVM vs. REVM: Quick Comparison

4. Dual-VM Architecture Overview

pallet-revive is an experimental smart contract pallet that executes contracts using two virtual machines:

• High-Performance Mode: Native RISC-V 64-bit execution engine using PolkaVM.
• Compatibility Mode: Ethereum bytecode compatibility layer using REVM.

The On/Off Switch

The AllowEVMBytecode setting is simply the switch that tells the system which mode to use:

• Switch = ON (true): The system runs in Compatibility Mode to welcome dApps from EVM-compatible chains.
• Switch = OFF (false): The system runs in High-Performance Mode to use Polkadot's own advanced engine.

5. Why This Dual Approach?

The strategy is pragmatic: quick adoption now, innovation later.

• Short-term (REVM first): By offering full Ethereum compatibility through REVM, Polkadot Hub can immediately attract existing Ethereum applications, users, and liquidity. This gets the ecosystem growing fast.
• Long-term (PolkaVM focused): Once the ecosystem has momentum, developers can gradually migrate to PolkaVM to benefit from the superior performance and lower costs.

6. The Practical Benefits

For users and developers, the dual-VM architecture means:

• For Ethereum Developers:
  • Easy migration: EVM’s compatible projects can move to Polkadot Hub almost instantly through REVM
  • Familiar dev tools , apps and knowledges
• For Polkadot Developers:
  • Building next-generation applications with PolkaVM with more advanced use-case
• For Users:
  • Better performance: Over time, apps can upgrade to PolkaVM for faster, cheaper execution
  • Growing ecosystem: More applications create more network effects, attracting more users and builders
  • Security: All applications get Polkadot's robust, shared security system regardless of which VM they use

7. Conclusion

This architecture represents Polkadot's balanced approach: bringing both immediate market adoption and long-term technical innovation to enable complex applications while maintaining the developer experience everyone already knows.

8. Resources

• Arbitrum Stylus: Gentle Introduction
• Avalanche: Virtual Machines
• Polkadot Forum: Prioritizing Ecosystem Growth (EVM)