| The amount of processing power required to mine bitcoins has made it essentially uneconomical for any individual to make money doing it. The only practical mining systems are running dedicated custom hardware (specially designed ASICs) in specially constructed data centers with cheap power.
The problem is serial, not parallel. Multiple computers could work on multiple bitcoins, but only one computer at a time could work on a single bitcoin, and the first computer to add the bitcoin to the ledger gets the reward; in other words, it's about who's got the fastest single-threaded system. That's what the custom ASICs are all about; they take the problem of computing the bitcoin hash (the proof of work) and attack it using specialized hardware dedicated to that one function, so they can do it very very fast. |