When it comes to building a cryptocurrency mining rig, the GPU is usually the star of the show. The most effective tool for mining is an advanced and powerful graphics processors, though there's still a role for the CPU to play. Bitcoin does require a fairly competent processor, but Application-specific Integrated Circuit (ASIC) processors have already been released and made available, undercutting Intel and AMD while offering better performance.
That said, if you plan to build a PC for mining, you need a processor. Here are a few options for you to consider.
Intel Pentium G4560
When putting together a rig you will solely use for cryptocurrency mining, an Intel Pentium is really all you need. Coming in at around $60, it's inexpensive, cheap to run and will make it easy to make a return. The only downside to choosing a processor in the Pentium range is the resale value of the machine if the currency mining doesn't play out. If you need to sell this PC to someone else, you're going to have a hard time finding someone to buy it as opposed to an Intel Core CPU.
It's the bare minimum that you'll require if you plan to use the PC as a computer afterward but is ample enough for mining, being a dual-core processor.
AMD Ryzen 3 2200G
The Ryzen 3 2200G is one of the newer processors released by AMD as part of the Ryzen line-up. These processors come rocking Vega graphics and while it's not quite as capable as a dedicated video card (especially for crypto mining), it does allow for use post-mining in games and as a traditional workstation. The CPU itself is an unlocked quad-core package.
This option is ideal if you plan to sell the PC after you're done with it, or use it as a casual gaming rig. Not bad for just under $100.
AMD Ryzen Threadripper 1950X
The father of all current generation processors. AMD's Threadripper line offers exceptional performance for the price, allowing budding cryptocurrency miners to really take things to the next level. 16 cores and 32 threads turns this processor into an absolute monster when paired with equally fast RAM, a capable motherboard and the best GPU on the market.
Much more than you need for an average computer, let along mining rig the Threadripper will enable the owner to smash through calculations in CPU-intensive mining. This processor will set you back around $900.
