These items are all related so it makes sense to consider them all together. Motherboards come in two main sizes, also known as form factors, they are ATX and micro ATX, as you will recall these are also sizes that we referred to when discussing cases and if you had taken my advice and gone for a larger ATX case you will be able to fit in either an ATX motherboard or a micro ATX motherboard. Deciding on a motherboard and processor is a bit like the chicken and the egg.
It all comes down to whether you want a particular motherboard or a particular processor. I usually pick the processor first by selecting a device that gives good performance for a good price. Once you’ve got that in place you can finalise your motherboard choice and then finally your memory, so let’s start with the CPU.