The PCI slot on your motherboard is fast becoming superseded.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.
| SLOT TYPE | SPEED |
| PCI | 1 Gbps |
| AGP 8X | 17 Gbps |
| PCI Express 1x | 2.5 [5]* Gbps |
| PCI Express 2x | 5 [10]* Gbps |
| PCI Express 4x | 10 [20]* Gbps |
| PCI Express 8x | 20 [40]* Gbps |
| PCI Express 16x | 40 [80]* Gbps |
| PCI Express 32x | 80 [160]* Gbps |
| IDE (ATA100) | 0.8 Mbps |
| IDE (ATA133) | 1 Gbps |
| SATA 2 | 3 Gbps |
*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