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Most PCs from the leading vendors now include at least one PCI Express slot. The most common slot sizes are x1 and x16. The x1 slot is a general-purpose slot that can host devices such as NI PCIe M Series data acquisition and NI PCIe GPIB devices. Currently, server-class machines are required for x4 and x8 slots which are used by devices including the NI PCIe Camera Link image acquisition device. “Server” does not imply high price, though, as tower servers are available for prices comparable to desktop machines. For example, as of May 2005, the Dell SC420 server has one x1 and one x8 PCI Express slot in addition to three PCI slots starting at $299 (USD).


Figure 4. Most motherboards have a combination of PCI and PCI Express slots

It is important when choosing a computer to make sure that the PCI Express connectors are wired to the physical connection size. For instance, some vendors use motherboards with x8 connectors that are wired as x4. Devices in these slots will only operate at x4 data rates. In the case that you are up-plugging a PCI Express device, make sure that the computer you are using supports up-plugging at the maximum data rate supported by your device. The PCI Express specification only requires up-plugging to operate at the x1 data rate. This could result in a x4 device that is plugged into a x8 connector to operate at x1 data rates (250 MB/s).