The bitcoin network is growing, so are the number of transactions. All bitcoin transactions are recorded in a ledger, in this case a decentralized one called Blockchain. The transactions happening over blockchain needs to be verified and miners are the ones who contribute the processing power for the algorithm to verify these transactions. In return miners receive rewards in the form of freshly minted bitcoin.
As the bitcoin network grows, the amount of processing power required to decrypt the information on blockchain and verify transactions also increases. Which in turn means, the miners contribution greater processing power will earn more. Bitcoin mining these days involve specialized hardware custom made for the application and these are called ASICs (Application Specific Integrated Circuits). Mining ASICs pack a lot of processing power and they consume a lot of power in return to churn it out. Many companies are currently involved in optimizing these ASICs with latest hardware architecture to create energy efficient and more powerful miners. Bitmain is one such company based out of Beijing, China.
Bitmain has recently introduced its latest mining ASIC labelled BM1385 which it claims