Bitcoin mining is the process through which bitcoins are released to come into circulation. Basically, it involves solving a computationally difficult puzzle to discover a new block, which is added to the blockchain, and receiving a reward in the form of few bitcoins. The block reward was 50 new bitcoins in 2009; it decreases every four years. As more and more bitcoins are created, the difficulty of the mining process – that is, the amount of computing power involved – increases. The mining difficulty began at 1.0 with Bitcoin's debut back in 2009; at the end of the year, it was only 1.18. As of April 2017, the mining difficulty is over 4.24 billion. Once, an ordinary desktop computer sufficed for the mining process; now, to combat the difficulty level, miners must use faster hardware like Application-Specific Integrated Circuits (ASIC), more advanced processing units like Graphic Processing Units (GPUs), etc.
Full clients verify transactions directly by downloading a full copy of the blockchain (over 150 GB As of January 2018). They are the most secure and reliable way of using the network, as trust in external parties is not required. Full clients check the validity of mined blocks, preventing them from transacting on a chain that breaks or alters network rules. Because of its size and complexity, downloading and verifying the entire blockchain is not suitable for all computing devices.