Bitcoin and Bitcoin Cash are two separate cryptocurrencies. They have different blockchains and therefore different rules. Bitcoin Cash is a fork of the Bitcoin blockchain. It was created in August 2017 in order to solve the problem of scalability on the Bitcoin blockchain.
Bitcoin Cash has a larger block size of 8 MB, which means that more transactions can be processed per second. Bitcoin Cash also uses a different mining algorithm, called SHA-256, which is more efficient than the mining algorithm used by Bitcoin.
BTCB is not the same as Bitcoin. BTCB is a token that is built on the Ethereum blockchain.
It is backed by real bitcoins that are stored in a reserve. BTCB holders can redeem their tokens for bitcoins at any time.