A: No, it's not. Although PCI-X sounds like it would be PCI-Express, it's actually a different standard and a completely different physical interface.
PCI-X stands for PCI-eXtended. It's an extended version of the original PCI and upgrades PCI from 32-bit to 64-bits. It has a much longer physical interface and also runs at 4 times the clock speed, raising the maximum data transfer of PCI-X to 1.06GB/s, instead of 133MB/s with standard PCI.
PCI-Express (PCIe) actually supersedes both PCI and PCI-X. PCIe has higher speeds, a smaller form factor of connections, and hot plugable capabilities. PCIe consists of a number of lanes with slots and devices supporting single lane (x1) and multi-lane (x4, x8, x16 and x32).
Each lane is four wires, enabling simultaneous bi-directional data transfer. Typically, you can place x1 devices in x4 and x8 slots (but potentially not in x16). Usually, x16 slots are used for 3D graphics cards and multi-port Gigabit NICs or 10 Gigabit NICs.
A x1 PCIe device is roughly the same speed as a PCI-X device. You might have slots that are x8 or x16 size but will be noted as x1 or x4 speed only, which means the slot size handles larger PCIe cards but will run only at x1 or x4 speed.
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