I/O modules, cards and boards accept data (input) from computers, sensors, transducers, or programmable logic controllers (PLC) and then distribute the data (output) to other devices in the system. Some I/O cards can perform simple computations on the input data before distribution; however, most devices distribute the data without processing. An I/O module varies in terms of the number of input channels and the number of output channels. I/O modules can have a large number of both. Many I/O modules are used for data acquisition in conjunction with personal computers (PC) and other computer processors or systems. Some I/O modules combine the functions of multiple I/O boards on a single I/O card. With these products, a single I/O card can perform four functions: analog output, analog input, digital output, and digital input. These versatile I/O modules, cards and boards are an integral part of data acquisition.