To fund the creation of Apple's first computer, Steve Wozniak and Steve Jobs sold... ATX (not in the list above). The most mainstream and common motherboard form factor, ATX was created by Intel ...

All four motherboard sizes support the latest and greatest of today's processor technology, just in different ways. Mini-ITX ...

It's a form factor that naturally draws quite a bit ... you'll notice that pretty much every motherboard now only comes with a single (usually reinforced by some "armor" or gimmick) PCIe x16 ...