Polkadot's JAM

Polkadot Virtual Machine (PVM)

The PVM is based on the RISC-V Instruction Set Architecture (ISA), valued for its simplicity and flexibility. RISC-V offers several benefits:

• Easily transpiled into common hardware formats such as x86, x64, and ARM.
• Strong support from tools like LLVM.

The PVM emphasizes simplicity and security, being sandboxable and providing various execution guarantees. It is deterministic, consensus-sensitive, and friendly to metering, avoiding the complexity found in other VMs.


Advantages over WASM:

• WASM, while optimized for web use, struggles with stack management and continuations.
• RISC-V places the stack in memory, handling continuations naturally without extra complexity.
• PVM achieves excellent execution speeds on conventional hardware (x64 and ARM), offering advantages like free metering compared to WASM.

RISC-V-enabled Continuations:

• Facilitates scalable coding on multi-core platforms like JAM.
• Asynchronous, parallelized architectures are crucial for scalability in hardware, software, blockchain, and consensus algorithms.

SAFROLE

SAFROLE is a simplified block production algorithm derived from SASSAFRAS. It:

• Is minimally opinionated to maximize potential future use cases.
• Aims to follow the Ethereum yellow paper model for wide implementation and expertise dissemination.

SAFROLE Features:

• SNARK-based, offering constant-time block production and near fork-free operation.
• Anonymity ensures the security of block production, preventing spam.

Networking

JAM uses the QUIC protocol, enabling direct connections between validators. This avoids gossip protocols as JAM doesn't handle transactions. Grid-diffusal is used for broader distribution, arranging validators in a grid for efficient package delivery.

Efficient Block Processing

JAM adopts a unique approach by placing the prior state root in the block header, allowing:

• Lightweight computations (5% of the block's workload) to be executed immediately.
• The remaining 95% of computations to be completed afterward.
• More efficient use of block time, improving computation time significantly over traditional setups.

Architectural Differences: JAM vs. Relay Chain

JAM fixes more functionality elements compared to the relay chain, making upgrades challenging but optimizing performance. Key differences include:

• Fixed parameters enable network topology and timing optimizations.
• Flexibility in application-level functionalities like coretime sales, staking, and governance managed within services.
• A non-upgradable chain reduces complexity.

JAM Toaster

A comprehensive test environment designed for large-scale trials and performance assessments of JAM, addressing challenges in understanding network dynamics at scale.

JAM and Substrate

Benchmarks vs. Metering:

• JAM's metered system can often replace frequent benchmarking.
• Benchmarking remains relevant for performance enhancements and tasks requiring extended execution times.

Cross-Chain Message Passing (XCMP)

JAM mandates full XCMP support for efficient data transmission between parachains, overcoming limitations of HRMP.

Accords

Accords are multi-instance smart contracts enabling direct, trustless interactions between parachains, enhancing token transfers and message integrity.

Enhancements and Compatibility in JAM

JAM maintains compatibility with Polkadot 1 parachains while introducing significant enhancements:

• Streamlined benchmarking.
• Multi-instance accords for governing parachain interactions.
• Full XCMP support.
• Agile Coretime targeting for efficient resource allocation.