What is the X4 slot for?

[geepondy]

First time in five or six years, I'm putting together a new system, so many aspects of the mb layout are new to me. I was wondering what the X1-X4 slot was and if any useful cards utilize it. I only have two precious PCI slots so if I end up getting something (like possibly an e-sata card), if I could save my PCI slots, that would be nice.

 

[Quiksilver]

For expansion cards that make use of the PCI-Express x4 (or X1) slots. Which I don't believe are too nay of them at the moment or at least that I have seen.

 

[Heidfirst]

Depends what mobo you have e.g. if it's a P35 chipset board then it can be used for a 2nd gfx card or in some boards a RAID card (some boards like the abit IP35 allow this but others apparently don't).
Or of course it can take any PCI-E card lower than x4.
For x1 PCI-E there are USB, Firewire, ethernet, wifi, parallel & serial port, SATA & PATA cards, TV cards & Creative have a PCI-E soundcard although it's not a proper X-Fi (even though it's labelled as if it is). Asus I believe are also planning a PCI-E x1 Xonar soundcard.