The PC Series Modules are broken into two distinct categories, PC-B and PCI. The PC-B modules plug into PC/AT/XT compatible ISA bus slots while the PCI modules plug into PCI slots. Both are available as either switch modules or driver modules. The modules can be controlled either by direct hardware port access or by installable device drivers. PCI modules come with plug and play device drivers. Software support is available for the most common program languages. The modules also have a special status feedback feature which enables the computer to confirm that the correct selections have been made by checking the relay drive. This can be used to self test the modules or as a diagnostic tool.