The sizes are x1, x4, x8 and x16. They support different bandwidth... Also x16 port might work in x8 mode only.
PCI Express currently comes in four different slot sizes; the longest size (PCI Express x16) and the shortest size (PCI Express x1) There are also The accelerated Graphics Port (AGP) and also Industry Standard Architecture. (ISA) :-)
pci express (PCIe)
Conventional PCI now has four types of slots and six possible PCI card configurations to use these slots
52
1
They each give a different bandwidth.Each lane of a PCI-X card gives you 1 GB of bandwidth.They come in 1,4, and 16 lane sizes
A 16 x PCI Express is better,but you may get a better deal with an AGP card.If you want the very best graphics then you use two 16x PCI express slots running SLI>
A pci and a pci-e are different ports. I would say no for sure. http://www.whatthetech.com/2007/11/10/can-pci-express-graphic-card-work-in-pci-slots/
The Compaq Presario CQ5210F has only one legacy PCI slot,but it has three PCI Express slots (1 x16 and 2 X1)
It is the next step up from pci....the longer slots, so in the future things like sound cards, network cards will fit these slots......
These slots are faster than the older PCI slots, making them more suitable for high-performance video cards.
In fact there are a huge variety of PCI Express video cards. If you plan on looking at some or even buying them, go to tigerdirect.com, click on PC Parts at the top, scroll down and click on PCI Express for video cards. I'm am most sure that this will be very helpful.