Taken from a website listed in my sources. " The Texas Instruments PCI7621 controller is an integrated dual-socket UltraMedia PC Card controller, Smart Card controller, IEEE 1394 open HCI host controller and PHY, and flash media controller. This high-performance integrated solution provides the latest in PC Card, Smart Card, IEEE 1394, Secure Digital (SD), MultiMediaCard (MMC), Memory Stick/PRO, SmartMedia, and XD technology." Basically it's a chip on your computer's motherboard that controls hardware like card readers and all the stuff listed above. That chip knows how to use those pieces of hardware when instructed to do so by the driver on the computer, it's like an interpreter I guess, probably not the best comparison ever but it has relevance.