The PCI slot on your motherboard is fast becoming superseded. It is being replaced by the PCI express slots. This will eventually mean than all your old cards will not fit into the new slots.

PCI express comes in a few varieties - 1x, 2x, 4x, 8x, 16x and 32x. The longer the slot, the faster the card. At the moment, 16x PCI Express graphics cards are pretty common.

*Dual direction

Gbps: Giga bits per second, (1,000,000,000 bps).
Mbps: Mega bits per second - (1,000,000 bps).
Byte: is 8 bits

PCI Express 1x Slot

PCI Express 16x Slot

Further Reading

• PCI Express Wiki
• Data Rate Units