A graphical user interface (GUI) is used to describe any type of digital interface that accepts input via a keyboard, mouse or similar device. They are most commonly found in computer systems, which of course features a monitor for output and keyboard/mouse combo for input. Of course, this is just one example of a GUI. You can find them in other applications, as well, both consumer and commercial-driven.
Human Machine Interface
Not to be confused with a GUI, human machine interfaces (HMI) differs in the sense that it focuses strictly on a mechanical means of input. HMIs are commonly found in factories and industrial settings, allowing human workers to control and/or manipulate machines through the input. To put the popularity of HMIs into perspective, researchers predict the market will grow to a whopping $5579.3 million by 2019. This growth is largely attributed to the increasing use of HMIs among industrial companies and product manufacturers.
Direct Manipulation Interface
As the name suggests, a direct manipulation interface allows for the manipulation of objects presented to the operator. According to Wikipedia, the term is closely associated with interfaces that rely on windows, icon, buttons and menus. The vast majority of direct manipulation interfaces contain at least some of these elements.
Touch User Interface
A touch user interface is an interface that supports touchscreen technology, complete with both input and output. Touch user interfaces can be found in standard PCs, as well as tablets, smartphones, and even custom devices. The user touches the interface to perform various commands, at which point the origin of his or her touch is identified and the device makes the appropriate output for the command. Touch user interfaces are often used in conjunction with haptics feedback for a higher level of accuracy and user satisfaction. With that said, however, haptics is a not a requirement for a working touch user interfaces, rather it’s a bonus feature.
Last but not least, a hardware interface is a type of physical interface that’s commonly found in real-world products like kitchen appliances, car dashboards, airplane cockpits, etc. They may feature knobs, switches, sliders and buttons, all of which provide a method of input so the operator can control the respective machine or device.