CPU mining was Bitcoin’s original approach. In the network’s infancy, you could run the Bitcoin client on a standard PC and occasionally earn new BTC when a block was found. Over time, as competition and hashing difficulty soared, mining moved to more specialized hardware—GPUs, then ASICs—making CPU mining nearly obsolete.

This progression reflects proof-of-work’s competitive nature: once mining becomes profitable, people invest in dedicated gear. Today, CPU mining is typically not feasible on Bitcoin unless you just enjoy hearing your computer fan spin like it’s training for a marathon.