pci whats the difference?

PCI started out as a parallel bus system ( typically white connectors, about 100mm long).

PCI Express is a newer, Serial bus system, (like USB or SATA but yet another protocol).

The 'x number' is the number of sets of serial links (or channels) on the connector, so a PCI Express x1 has a single serial bus, whereas a x16 has sixteen separate serial bus links that can work simultaneously to transfer that much more data than a x1 system.

Some i/o cards use x4 or x8 buses, the connectors are designed so you can also fit any smaller card in a larger slot - so a x4 will work in a x16 slot.

The x16 slots are normally used for video cards, but gradually motherboards are including additional connectors for multiple video or other fast peripherals (eg. 10GBit ethernet or Infiniband cards can use eight channels).

Look at it this way...when PCI slots came out,they had a certain "rating" in speed. You could say that PCI standard would be x1 speed ...then there is the PCIe or an "express" slot at x16..or 16 times faster than the PCI slot ..its just used for graphics as you would want your graphics to keep up with faster speed of the newer CPU's. then a short slot in PCI came out so it was called the PCIe (express) x1 slot which would have the same speed as the PCI slot, just shorter. Then the PCIe x4 slot which is the shorter slot but 4 times as fast as the PCIe x1 slot. Its just a matter of speed and bandwidth. the "versions" of PCIe x16 slots are, 1.0/1.1 with a speed (bandwidth) of 2.5GT/s (gigatrasnsfers per second) the version 2.0 has 5GT/s as does the version 2.1 but with some overhead telemetry to bring it in line with version 3.0 when it comes out. Since PCI is an "old" standard there is less of them than there use to be the PCI express x1 and x4 are taking there place. Just like you no longer see IDE or floppy ports on a mother board as the SATA has taken the IDE ports place as it is 2 to 4 times faster than IDE and a USB flash drive can hold more data than a floppy and is much faster too!

PCI slots were created during the 32-bit era and are now limited to speed performance.

PCI-Express is the cure for the faulty and unreliable AGP technology graphic display from a few years back.

True story, I was watching a dual layer dvd movie from the PC and the AGP card was completely covered in flames at about 50 mins into the movie.

I was watching 'Leon: The Professional' and the card caught on fire trying to decode the fast moving action scenes.

PCI-Express are extremely stable and reliable and you don't have to worry about your PC catching on fire.

most current graphics cards use PCIe x16, older cards used the smaller pcie, and even older cards used PCI