Public Blockchain

What Is Public Blockchain?

A blockchain is a digital ledger to take notes of transactions. The blockchain expands as new sets of recordings are added. A block consists of the previous block's cryptographic hash, a timestamp, and transaction data. Bitcoin nodes use the blockchain to identify genuine Bitcoin transactions from attempts to re-spend previously spent coins elsewhere.

Anyone with an active connection can send transactions on it and become a validator (i.e., participate in executing a consensus protocol). Bitcoin is one of the largest public blockchains. A private blockchain is permissioned. Only a selected group of people can access it, and there are known participants. Stanford University's Computer Science department guest lectures discuss use cases for private blockchains. 

R3 is a consortium of over 200 financial institutions developing Corda, a private blockchain platform for business transactions. A consortium blockchain is also permissioned, but instead of a single organization controlling it, a consortium does. Consortium chains are often referred to as "semi-private" blockchains. This is because they lie between public and private blockchains regarding the level of decentralization. 

A public blockchain is basically a decentralized ledger that anyone can download and run. Public blockchains are often permissionless, meaning anyone can participate without needing to be approved by a centralized entity. Bitcoin and Ethereum are examples of public blockchains in cryptocurrency.