I'm new-ish to Arduino, and I wanted to see what hardware does it use. So I looked at the Arduino's schematics, and noticed some odd things. My problem is that I never worked with PCB design, I just know how to read basic schematics, containing just resistors, capacitors, coils, flip-flops, and small ICs (like 555). And what seemed odd to me is that there are several nets (circuits) which aren't all connected together. On this image I circled the separated circuits, and on the other is the whole image itself. There is a link down there for the schematics.