Blockchain enables industries to go out of the box where there is no trusted single entity who is maintaining data ie digital data which is also reffered as Gold. Key features of blockchain is decentralization.
Decentralization is a property which utlizes the concept of peer to peer model and allows fragmented parties to communicate with each other using modern standard of cryptography.
Full nodes relay transactions to miners.
Performs various user related / wallet related queries.
Bitcoin and Ethereum use Nakamoto Consensus to regulate transactions in blockchain.
Bitcoin produces a block every 10 minutes which is relayed to peers using flooding technique and is size of 0.99 MB. Uses TCP to establish connection with other peer/clients.
Ethereum uses chain selection rule alongside GHOST protocol and achieves block production in about 10 to 20 seconds and is dependent of fees provided by the user known as Gas. It employs UDP based node discovery.
Now mining ETH and BTC with such difficulty with commodity hardware is not going to be feasible. In case of BTC 53 % of hash power is controlled by four top miners, and in ETH top three controls 61 %.