correctly can cause a resource conflict and lead to erratic behavior. PC/104-Plus The PC/104-Plus standard adds support for the PCI bus, in addition to the ISA bus of the PC/104 standard. The name is derived from its origin: a PC/104-Plus module has a PC/104 connector (ISA) plus a PCI connector. The standard defines a 120-pin connector for the PCI bus, located on the opposite side of the board from the PC/104 connector. PC/104-Plus CPU boards provide active communication on both buses, and are capable of communicating with both ISA and PCI peripheral cards. On PC/104-Plus peripheral modules, the PC/104 connector is simply a passive connector for stackability; the module actively communicates on the PCI bus only. As a corollary, a PC/104-Plus peripheral module may not be used with a PC/104 CPU board. However, a PC/104-Plus CPU board may be used with a PC/104 peripheral module. Since PC/104-Plus is based on PCI, there is no need to set a Base Address, IRQ, or DMA channel on the peripheral boards. However, it is necessary to specify the PCI Slot Number of a peripheral board when it is installed. This is commonly set by a rotary switch, DIP switch, or jumpers on the peripheral board. Each PCI peripheral board in the system must have the PCI Slot Number set to a unique value. Failure to do so may cause erratic system behavior. The peripheral closest to the CPU should be set for the first slot, the next board should be set for the second slot, etc. PCI-104 The PCI-104 form factor includes the PCI connector, but not the PC/104 connector, in order to increase the available board real estate. Even though the PCI connector has 120 pins instead of 104, the established name was kept. The PCI connector location and pinout is identical to PC/104-Plus. Since the ISA bus is omitted, a PCI-104 board is incompatible with PC/104 peripheral module. However, PCI-104 and PC/104-Plus are compatible, since they both utilize the PCI bus. Most PC/104-Plus boards can be manufactured as PCI-104 by simply not populating the PC/104 connector. PCI-104 utilizes the same PCI Slot Number selection scheme as PC/104-Plus. Each device must be assigned to a unique slot number. PCI/104-Express The PCI/104-Express specification incorporates the PCI Express bus (PCIe) in addition to the previous-generation PCI bus. The specification defines a 156-pin surface mount connector for the PCI Express signals. The new connector occupies