Here the consensus mechanism is Proof of Work and the release method when it started was through "genesis block mined".
Here the algorithm is SHA-256, mining are ASIC miners.
The block time is 10 mins.
It has issues of scalability, however latest development like segwit, lightning network is aims to improve the scalability.
The cryptocurrency that is used in BTC Blockchain is BTC(Bitcoin).
It aims to offer a world wide decentralized distributed technology through which digital currency can be sent with out a third party and through peer to peer transaction.
It is the first ever decentralized blockchain technology released in the year 2008 & the founder is Satoshi Nakamoto.
Here the consensus mechanism is Proof of Work and the release method when it started was through "presale".
Here the algorithm is Ethhash and mining are GPUs.
Block time is 12 seconds.
It offers better scalability than BTC blockchain and with recent second layer development like plasma, raiden it aims to improve its scalability further.
The cryptocurrency that is used in ETH blockchain is ETH.
It aims to offer more than just a cryptocurrency transaction and it offers a decentralized platform for running dApps and smart contracts which can be coded by programming language like solidity. It offers the enterprise level adoption of blockchain technology.
The ETH blockchain technology was released in the year 2015 and the founder is Vitalik Buterin.