There is only one public Ethereum mainnet. Applications that are built on the mainnet are able to interoperate, similarly to how applications built on the Internet can connect to each other, leveraging the full potential of decentralized blockchain.

Many businesses and consortia have deployed private, permissioned blockchains for specific applications based on Ethereum technology.

Key differences

• Blockchain Security/Immutability – A blockchain’s resistance to tampering is determined by its consensus algorithm. Ethereum mainnet is secured by the interaction of thousands of independent nodes run by individuals and miners throughout the world. Private chains typically have a small number of nodes which are controlled by one or a few organizations; those nodes can be tightly controlled, but only a few must be compromised in order to rewrite the chain or commit fraudulent transactions.
• Performance – Because private Enterprise Ethereum chains may use high performance nodes with special hardware requirements and different consensus algorithms such as Proof of Authority, they may achieve higher transaction throughput on the base layer (Layer 1). On Ethereum mainnet, high throughput can be achieved with the use of Layer 2 scaling solutions.
• Cost – The cost to operate a private chain is primarily reflected in labor to set up and manage the chain, and the servers to run it. While there is no cost to connect to Ethereum mainnet, there is a gas cost for every transaction which must be paid for in Ether. Transaction relayers (aka Gas Stations) are being developed in order to eliminate the need for end users and even enterprises to directly use Ether in their transactions. Some analyses have shown that the total cost to operate an application may be lower on mainnet than running a private chain.
• Node Permissioning – Only authorized nodes can join private chains. Anybody can set up a node on Ethereum mainnet.
• Privacy – Access to data written to private chains can be controlled by restricting access to the network, and on a more fine grained basis with access controls and private transactions. All data written to mainnet Layer 1 is viewable by anyone, so sensitive information should be stored and transmitted off-chain, or else encrypted. Design patterns that facilitate this are emerging (e.g. Baseline, Aztec), as well as Layer 2 solutions that can keep data compartmentalized and off of Layer 1.