Computer Noob :D What's a PCI bus?

I’m exploring my laptop, and stumbled upon device manager. I expanded system devices, and I saw this thing called "PCI bus", "PCI Host CPU Bridge", and "PCI Standard ISA bridge." What are those? Extra question: I also saw somewhere system devices "SiS PCI Express x1, x16 Root Ports". Do they have anything in relation with [...] http://bit.ly/r69K2J