[CentOS] OT: PCI express questions???

We have several DELL servers run under CENTOS 5.  I check server spec and found some servers expansion slot say PCIE and some say PCIE generation 2.

My questions are:

1. does PCI express meaning PCIE 1.0???

2. does PCIE generation 2 same like PCIE 2.0???

3. what is speed on following:

PCI  X4:
PCI  X8:

PCI generation 2 X4:
PCI generation 2 X8:

Thanks.