PLC software is used to create the computer program that is stored in a PLC to make it monitor its inputs and control its outputs. Once a PLC has its program loaded, it runs on its own. The PLC software can also be used for maintenance purposes. Each PLC program is typically unique to the specific machine or equipment it is controlling. Installed on a computer (i.e. PC), PLC software is typically used by an engineer who is responsible for programming the PLC to do its task.