A blockchain that can be accessed by anyone.
A public blockchain is a decentralized platform accessible by anyone. In other words, it is permissionless, meaning anyone can join, write and read the information on the platform. A blockchain is a distributed ledger where transaction data is packaged and stored in the form of blocks.
Therefore, a combination of these “blocks” forms a blockchain. A key factor that differentiates one block from the other is the timestamp. Once validated, data stored on the platform can’t be altered despite being publicly available.
A public blockchain uses a consensus mechanism to validate transactions. The leading two public blockchains, Bitcoin and Ethereum, use the proof-of-work (PoW) consensus mechanism. However, Ethereum has started the journey to transition into a proof-of-stake (PoS) consensus mechanism.
A public blockchain offers greater transparency compared to private networks, and is more decentralized since anyone can join and no single entity has control over the whole system. Unfortunately, a lot of public blockchains also suffer from low transaction speeds and other scalability issues. Furthermore, a public blockchain is also limited to a few consensus mechanisms compared to a private blockchain.
A private and public blockchain are similar in the sense that each node on their network has an exact copy of their ledger, their stored data is immutable and both platforms rely on transaction validators.