Re: what is a pci card..?
PCI card is simply a card that fit into a PCI slot.
PCI standard is well-defined, up to the connector.
PCI bus have it's advantages over older ISA/EISA bus as it is faster, but can also support request from any of the interfaces to any of the interfaces.
For example, in the older ISA bus structure, the CPU was the master, and all ISA interfaces (cards) were slaves. The CPU made request to the cards, and the cards just answered the requests.
In PCI, you can have the CPU talking to a card, but you can also have a card talking directly to another interface. A good example is some PCI video card, which use off-board (shared) memory. The CPU tell the card where to get it's pixel data, and then, the card read the data directly from the mainboard memory, without any intervention from the CPU.
Older (ISA) cards achieved similar process via the use of DMA. Though, the CPU was responsible for programming the DMA, and initiating the transfer. With PCI, there's no more need for DMA, and the process doesn't even require the CPU to be aware. Transactions are transparent to the CPU.