Expansion Bus Types Expansion slots provide a connection for a number of devices and functions, some internally on the motherboard and a couple externally. The following table lists common expansion buses in a PC system: Slot Characteristics ISA is a 16-bit I/O bus slot (a second short slot for additional 8-bits) that includes DIP switches and jumpers. ISA slots can be found on machines Industry Standard ranging from 286 models through Pentium models. ISA buses were used to Architecture (ISA) connect peripheral cards to the motherboard, but have been replaced by a newer bus called EISA (Extended ISA), which has a 32-bit bus. Supports a 32 or 64-bit I/O bus providing compatibility with both 486 and Pentium machines. • Peripheral Component Interconnect (PCI) • • • Mini-PCI This bus is processor independent (the CPU and the PCI bus can process concurrently). The PCI bus can support ISA and EISA (if PCI and ISA share a bus, then the use of one disables the other). PCI is plug-and-play. PCI buses are most commonly used for devices such as sound cards, modems, and network cards. Small form factor computers, such as laptops or micro-ATX systems, might include a mini-PCI slot. Mini-PCI devices are small cards with either 100or 124-pins. A typical use for a mini-PCI slot is to add internal cards (such as wireless cards) to laptops. PCI Express (PCIe) is a next generation I/O bus architecture. Rather than a shared bus, each PCIe slot links to a switch which prioritizes and routes data through a point-to-point dedicated connection and provides a serial fullduplex method of transmission. Peripheral Component Interconnect Express (PCIe) • • • • Accelerated Graphics Port Basic PCIe provides one lane for transmission (x1), at a transfer rate of 2.5 Gbps. It can also provide multiple transmission lanes (x2, x4, x8, x16, x32). In addition to greatly increased speed, PCIe offers higher quality service. PCIe is backwards compatible and allows legacy PCI technology to be run in the same system. PCIe buses are most commonly used for video cards in modern computer systems. Similar to PCI, but designed specifically for graphics support. Motherboards that provide AGP support have a single AGP slot. AGP is commonly used (AGP) for video cards in modern computer systems, but is being replaced by PCIe.