On PCI combo cards, there are normally two to four PCI devices behind the bridge on the card. These PCI devices include USB, Firewire, and Ethernet I/O chips as in this example; other combo cards include RS 232, MIDI, SPDIF, TV Tuners, MPEG Decoders and Encoders, Audio Processors, and other multimedia devices. The PCI Specification allows each PCI slot only one device load. In order for multiple devices to reside on the card, the PCI 6140 provides the lowest-cost isolated PCI bus on its secondary. This bus can handle up to four PCI devices at 33MHz.