8 minutes

The key distinction between public and private blockchains is access. A public blockchain is completely open, allowing anyone to participate in or audit its activities. It is truly a decentralized, authority-free operation. A private or “permissioned” blockchain, on the other hand, controls who participates and who can view transactions, allowing only selected and verified participants to execute consensus protocols and maintain the shared ledger, for example. 

In addition, the owner of a private blockchain can override, edit or delete entries on the blockchain; whereas entries on a public blockchain are immutable.  

Main differences:

Public Blockchain Private Blockchain
Decentralized peer-to-peer network  Not decentralized because mining capabilities and the system of consensus are centralized in the owner/operator’s hands
Data modification is not possible (immutability) Owner/operator may modify data
Anyone can join the network Only selected/verified participants can join the network
Anonymous participants Identified participants
No access control for sensitive information Security and confidentiality
Each node keeps the replica of the blockchain Scope of replication depends of the network and its rules
Proof of Work or Proof of Stake mechanism More complicated consensus algorithm, sometimes based on the user role
Relatively slow Relatively fast
Significant power consumption Lower power consumption