Polkadot JAM Explained. Simply!


Dr. Gavin Wood wrote the Ethereum Yellow Paper in 2014, followed by the Polkadot White Paper in 2016.

In April 2024, he released the JAM Gray Paper.

What is JAM, you might ask?! Let’s figure it out together in a simple way.


  1. Understanding the blockchain landscape: From Ethereum to Polkadot
  2. Why JAM is needed?
  3. JAM: Combining Ethereum with Polkadot
  4. JAM explained: A deeper dive
    4. 1.
    Key features of JAM
    4. 2.
    JAM performance target
  5. JAM prize & JAM toaster
  6. Conclusion: JAM as a promising future for scalable blockchains

1. Understanding the blockchain landscape: From Ethereum to Polkadot

First, let’s analyze those two blockchains that Dr. Gavin Wood created. We can use a simple example. Imagine a busy city with two key areas.

Downtown (Ethereum)

Bustling with activity, Ethereum allows various applications (Smart Contracts) to run on its main street (Blockchain). However, this traffic often leads to congestion and delays. Ethereum is limited by the throughput and by rising gas fees.

City districts (Polkadot)

Polkadot offers a network of independent communities (Parachains) connected to a central hub (Relay Chain). Each district has its applications (Smart Contracts) running, similar to how different neighborhoods. This allows for more applications, sharded scalability and all of them with independent logic and rules. But there is a need for public transport (XCM), to move between suburbs and with a central hub.

2. Why JAM is needed?

While Polkadot’s relay chain boasts significant processing power, its current architecture limits the types of services it can support. Think of it again like our bustling city, be it New York City. While Manhattan (Relay Chain) has the infrastructure to handle heavy traffic, its streets are designed specifically for independent communities (Parachains).

This means developers need to jump through additional hoops to run services outside the parachain model. JAM (Join-Accumulate Model) aims to streamline this process by making the relay chain more versatile. Here’s how:

  • Increased Flexibility: JAM removes the current limitations on the types of services that can run directly on the relay chain. This opens the door for a wider range of applications, not just parachains.
  • Developer Friendly: JAM simplifies deployment for developers. They only need to specify specific functions (refine, accumulate, and ontransfer) to get their service up and running. This reduces development complexity compared to the current parachain model.
source: Polkadot wiki

The outer districts (Parachains) offer sufficient space and flexibility for a variety of uses. However, their seamless integration with the Manhattan/central hub (Relay Chain) and other districts requires efficient means of transport, such as HRMP or later XCMP (Cross-Consensus Message Passing).

This limitation results in fewer applications running seamlessly, in contrast to the single-state environment of Ethereum (L1), where ERC20 tokens and smart contracts coexist effortlessly. As a result, the importance of integrating the XCMP protocol becomes more apparent.

JAM is the proposed solution to transform New York City (Polkadot) into a smoothly functioning mega-region.

3. JAM: Combining Ethereum with Polkadot

To get a bigger picture, let's analyze the current state of Ethereum and Polkadot.

Ethereum is a blockchain that allows the execution of smart contracts, enabling secure and automated agreements, and its potential for scalability through L2 solutions such as ZK-rollups.

Polkadot goes beyond Ethereum by offering the interconnection of appchains (aka Parachains), which can host smart contracts and have different tokenomics and computational logic. At the heart of this model is a Relay Chain that provides shared security for all parachains (technically, parachains are rollups to Polkadot) and allows them to connect via XCM (short for Cross-Consensus Message Format).

JAM aims to be a comprehensive, semi-coherent blockchain platform, combining Ethereum’s smart contract functionality with Polkadot’s parachain architecture for shared security, while offering native ZK-rollups for scalability, unlike Ethereum’s current reliance on separate L2 ZK-rollup solutions.

4. JAM explained: A deeper dive

JAM, which stands for Join-Accumulate Machine, is the cheapest possible safe decentralized system. It’s designed to replace the current Relay Chain, taking away all its functionalities such as staking or governance.

4. 1. Key features of JAM

  • Transactionless environment: JAM introduces an innovative paradigm — a transactionless ecosystem. While JAM itself operates without transactions, applications deployed on the platform are anticipated to handle transactions initiated by users, offering functionalities beyond traditional blockchain transactions. Apps can keep running as long as you provide them with DOT to run.
  • Multi-core computation: JAM enables parallel processing, allowing Polkadot to handle hundreds of chains and various programs simultaneously. This and elastic scaling will be most likely enabled on the Relay Chain even before JAM.
  • Smart Contracts & ZK-rollups: JAM differentiates itself by seamlessly integrating smart contracts and ZK-rollups, offering enhanced functionality and scalability. Most importantly, JAM’s smart contracts have the unique ability to operate autonomously and interact with the external environment independently, a feature not found in Ethereum, where user actions or bots are typically required to initiate smart contract functions. In addition, JAM stands out for its support of the UTXO model, which is similar to Bitcoin’s accounting framework.
  • SAFROLE, a SNARK-based block production algorithm: Derived from SASSAFRAS, it simplifies certain components to maximize potential future use cases. Great for anonymity features and is almost entirely fork-free.
  • XCMP importance: Full implementation is required for the operation of JAM to ensure that Proof of Validity (PoV) sizes remain manageable and in line with the platform’s normalized execution framework, leaving no room for arbitrary limit adjustments.
  • DOT token: DOT remains crucial for core time purchases, but JAM might significantly expand how core time can be utilized. The future of tokenomics is yet to be determined.
The JAM Data Topology resembles flower petals, representing general stateless machines, source
The JAM Anatomy of each petal, source

4. 2. JAM performance target

  • 350 JAM cores: JAM will support ~350 cores with 6s execution time & 5Mb input each, totaling around 2.3Gbps. Think of 1 core = 1 parachain for simplicity. This means 3x the current parachain computation!
  • Throughput 850MB: Comparing JAM to other blockchains, Ethereum 2.0 processes 1,3MB/s, Sui & Aptos 100 MB/s, Solana’s current version is 125 MB/s and after the Firedancer update up to 1250 MB/s according to VanEck blog. This puts JAM at an absolute high compared to most current blockchains.
source: VanEck blog

5. JAM prize & JAM toaster

JAM Prize: 10M DOT

The JAM Prize, funded by the Web3 Foundation Team, aims to jumpstart innovation by incentivizing developers to implement the JAM protocol in various ways.

The prize offers rewards across different tiers and programming languages, encouraging diverse implementations that contribute to the overall functionality of the JAM network.

Gavin Wood at Token2049, source

JAM Toaster

The JAM Toaster tackles a challenge faced during Polkadot development — understanding unexpected network behavior. This emulator helps by simulating a full-scale JAM network with 1,023 nodes operating at near capacity.

Packed with robust infrastructure and logging capabilities, the JAM Toaster allows developers to test and optimize their JAM implementations, ensuring a smooth-running final network. The toaster boasts impressive hardware specs, including 16,384 AMD CPUs, 16 GB of L2 cache, 32 TB of RAM, 20 PB secondary storage and extensive networking capabilities.

The Polkadot Palace

Also, there is an ecosystem facility under development in Lisbon called The Polkadot Palace, which will play host to a 12,276 core, 16 TB RAM super-computer capable of hosting the full JAM network in its entirely.

6. Conclusion: JAM as a promising future for scalable blockchains

It’s still early days for JAM, with about two years before it’s fully ready and deployed. When it is, it could be a powerful tool for developers, combining the strengths of smart contracts and Polkadot’s unique structure of parachains. JAM could lead the path of blockchain innovation.

By enabling multi-core processing, smart contracts, native ZK-rollups, and groundbreaking transactionless applications, JAM paves the way for a more powerful and versatile blockchain platform, having an outstanding 850 MB/s throughput and thus handling over 3,4M TPS. JAM is a highly ambitious project with the potential to transform the Polkadot ecosystem and blockchain technology as a whole.

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