Human Machine Interface software is often driven by the hardware selected, such as operator interface terminal (OIT), embedded PC or PC-based. Often the hardware selection simplifies the HMI software development. Not until the decision to go with PC-based HMI do the HMI software possibilities open up.
The definition of an HMI is wide-ranging. Certainly anything with a graphical display that an operator can interact with can be called an HMI. Even a one-line alphanumeric display can be an HMI and can display operator-selected information, such as fault messages or production counts. In many cases, when the HMI is specified, the HMI software is chosen by default—it comes with the hardware—although many vendors require the development software be purchased separately. HMI software is often application-driven, and there is a lot of overlap in the choices available