Public blockchains like Bitcoin where anyone can download the software, the previous transaction history, and start participating as a node are very different t

Public blockchains like Bitcoin where anyone can download the software, the previous transaction history, and start participating as a node are very different than the private blockchains you are asking about. Check out this blog post for a few ways companies are trying to solve private validation - http://sammantics.com/blog/2016/3/6/how-transactions-are-validated-on-a-shared-ledger http://sammantics.com/blog/2016/3/6/how-transactions-are-val...