"I want to interface my 8051 module with PCI bus on a PC motherboard, I heared that needs a PCI Interface??,"

Well, yeah -- if you want to interface to the motherboard's PCI bus, you need a PCI interface. The better question: exactly what do you want to accomplish?

"**I want to know exact what is the PCI interface? "

Go to your favorite online bookseller and search for "PCI System Architecture," published by MindShare. It's as close as you can come to the actual spec without springing the coin for the spec (which you WILL do if you do serious PCI development).

Note that this book is as thick as your local telephone book, although with somewhat larger type size.

"I heared about a card that is be put in a PCI slot on the motherboard and connect my module through an IDE cable,
**IS this realy a PCI interface or what?"

Um, that sounds like an IDE interface, which is a whole other ball of wax.

Again, what's your design intent?

=a