Machine controllers and monitors use electronic numeric control and monitoring interfaces for programming and calibrating computerized machinery. They are available in form factors such as card, desktop, DIN rail, embedded, handheld, panel mounted, and rack mounted. Machine controllers and monitors with a card form factor are designed to be plugged into a backplane. Desktop or standalone devices are sometimes described as towers. Machine controllers and monitors that are designed for mounting on a DIN rail or meant to be embedded used in many applications. Handheld, portable, panel mount, and rack mount devices are also commonly available.

Machine controllers and monitors have electrical, drive, memory, and application specifications. Electrical ratings include AC supply voltage, DC supply voltage, and AC input frequency (50, 60 or 400 Hz). Drives are defined by resolution, number of axes, and drive power. Resolution is the number of binary digits (bits) that machine controllers and monitors use characterize an analog signal. The number of axes that the device can drive or control varies. Often, follower or dependent axes are listed as "half" axes. Drive power is specified in either watts (W) or horsepower (hp). With regard to memory, the most important specifications are random access memory (RAM) and Flash RAM. Machine controllers and monitors are used in aerospace, automotive, marine, medical, military, and general industrial applications.

Selecting machine controllers and monitors requires an understanding of available features. Some devices resist vibration, include integral software, track up time and downtime, and serve as a data logger or recorder. Others are capable of multi-speed operation, and use optical isolation to protect inputs and outputs. Machine controllers and monitors that provide encoder feedback are also available. As a rule, proportional, integral and derivative (PID) control requires real-time system feedback. Machine controllers that are Web-enabled or GPS-enabled are designed for use with the Internet or with satellite-based global positioning systems (GPS).  

In terms of communication, machine controllers and monitors differ with regard to set up and control as well as communication standards. Choices for setup and control include computer interface, control panel, dial up, removable disk, handheld controller, joystick, manual, PCMCIA, and wireless communications. There are many different communication standards for machine controllers and monitors. These include ARCNET, AS-i, Beckhoff I/O, CANbus, CANopen, DeviceNet, Ethernet, IEEE 1394, IEEE P1451, FOUNDATION Fieldbus, GPIB, SCSI, SDS, SERCOS, Seriplex, TTL, USB, and VMEbus. Proprietary standards for machine controllers and monitors include FireWire (Apple Computer, Inc.), INTERBUS (Phoenix Contact GmbH & Co), PROFIBUS (PROFIBUS International), and Sensoplex (Hans Turck GmbH & Co.).