 While proof of work is an effective means of securing a blockchain, it inherently promotes competition amongst miners seeking higher and higher hashrates due to the rewards earned by the node who wins the right to add the next block. In turn, these higher hash rates benefit the blockchain, providing better security when it's a result of a well distributed/decentralized network of miners. When Bitcoin first launched its genesis block, it was mined exclusively by CPUs. Over the years, various programmers and developers have devised newer, faster, and more energy efficient ways to generate higher hashrates; some by perfecting the software end of things, and others, when the incentives are great enough, create expensive specialized hardware such as ASICs (application-specific integrated circuit). With the express purpose of extracting every last bit of hashing power, efficiency being paramount, ASICs are stripped down, bare minimum, hardware representations of a specific coin's algorithm. This gives ASICS a massive advantage in terms of raw hashing power and also in terms of energy consumption against CPUs/GPUs, but with significant drawbacks of being very expensive to design/manufacture, translating to a high economic barrier for the casual miner. Due to the fact that they are virtual hardware representations of a single targeted algorithm, this means that if a project decides to fork and change algorithms suddenly, your powerful brand-new ASIC becomes a very expensive paperweight. The high costs in developing and manufacturing ASICs and the associated risks involved, make them unfit for mass adoption at this time. Somewhere on the high end, in the vast hashrate expanse created between GPU and ASIC, sits the FPGA (field programmable gate array). FPGAs are basically ASICs that make some compromises with efficiency in order to have more flexibility, namely they are reprogrammable and often used in the "field" to test an algorithm before implementing it in an ASIC. As a precursor to the ASIC, FPGAs are somewhat similar to GPUs in their flexibility, but require advanced programming skills and, like ASICs, are expensive and still fairly uncommon. 