Relay Chain & Parachain
Polkadot is the sharded blockchain where processing nodes are separated into several shards, enabling parallel processing and solving scalability problems. Polkadot’s founders called this network the Relay chain and processing nodes the parachain.
Collators & Validators
Collators will collect the processed data from each shard and send them to be validated by the validators before distributing this data throughout the Relay Chain.
This technology will solve the interoperability problem of the blockchain. These bridges will connect another blockchain like Ethereum or Bitcoin to the Relay Chain in the process called bonding.
For the first time, Polkadot promised the upgradable blockchain without causing a hard fork. The hard fork is caused when developers of a blockchain have different opinions and decide to go in their own ways causing blockchain to split into 2 like Ethereum and Ethereum Classic, or Bitcoin and Bitcoin Cash, etc.