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System Chains

The primary functionality of the relay chain is to secure the parachains and facilitate secure communication between them. All other functionalities like asset transfers, governance, identities and bridging (a potentially resource intensive task) can benefit from operating separately on system chains. System chains are responsible for delegating functionality away from the relay chain for peformance reasons, taking advantage of the inherent parallelization the architecture of Polkadot provides.

Overview​

System parachains are those that contain core Polkadot protocol features, but in parachains rather than the relay chain. Rather than purchasing coretime on a marketplace, execution cores for system chains are allocated through the network governance.

By hosting core protocol logic in parachains instead of the relay chain, Polkadot uses its own scaling technology -- namely, parallel execution -- to host itself. System parachains remove transactions from the relay chain, allowing more relay chain blockspace to be used for Polkadot's primary purpose: validating parachains.

System parachains always defer to on-chain governance to manage their upgrades and other sensitive actions. That is, they do not have their own native tokens or governance systems separate from DOT KSM. In fact, there will likely be a system parachain specifically for network governance.

note

In the past, these were often called "Common Good Parachains", so you may come across articles and discussions using that term. As the network has evolved, that term has been confusing in many cases, so "System Parachains" is preferred now. A discussion on this evolution can be found in this forum thread.

Existing System Chains​

Asset Hub​

The Asset Hub on both Polkadot and Kusama are the first system parachains.

The Asset Hub is an asset portal for the entire network. It helps asset creators (e.g. reserve backed stablecoin issuers) to track the total issuance of their asset in the network, including amounts that have been transferred to other parachains. It is also the point where they can transact, to mint and burn, to manage the on-chain asset.

The Asset Hub also supports non-fungible assets (NFTs) via the Uniques pallet and the new nfts pallet. For more information about NFTs see the dedicated wiki page.

This logic for asset management is not encoded in smart contracts, but rather directly in the runtime of the chain. Because of the efficiency of executing logic in a parachain, fees and deposits are about 1/10th of their respective value on the relay chain.

These low fee levels mean that the Asset Hub is well suited for handling balances and transfers as well as managing on-chain assets.

Collectives​

The Polkadot Collectives parachain was added in Referendum 81 and exists only on Polkadot (i.e., there is no Kusama equivalent). The Collectives chain hosts on-chain collectives that serve the Polkadot network.

Some of these collectives are the Polkadot Alliance and the Polkadot Technical Fellowship. These on-chain collectives will play important roles in the future of network stewardship and decentralized governance.

Networks themselves can act as collectives and express their legislative voices as single opinions within other networks. This is achieved with the assistance from a bridge hub.

Bridge Hub​

Before Polkadot and Kusama supported their first parachains, the only way to design a bridge was to put the logic onto the relay chain itself. Since both networks now support parachains, it makes sense to have a parachain on each network dedicated to bridges. This is because of the execution isolation provided by parachains.

The Bridge Hub system parachain operates on the relay chain, and is responsible for faciliating bridges to the wider Web3 space. It contains the required bridge pallets in its runtime, which enable trustless bridging with other blockchain networks like Polkadot, Kusama and Ethereum. The Bridge Hub uses the native token of the relay chain.

See the Bridges page for information on the latest bridge projects.

People Chain​

The People Chain allows users to mange their account identity.

Coretime Chain​

The Coretime system chain allows users to buy coretime to access Polkadot's computation. Coretime marketplaces run on top of the Coretime chain. For more information about agile coretime, see here.