Originally, the term “dongle” was applied to any external attachment to a PC or one of its components. It seems to have originated in the UK and may have been coined to describe something which “dangled”, or hung, from the back of a machine.
These days, the term is normally applied only to devices, which may also be known as a “key”, “lock” or “sentinel”, designed to prevent software piracy. They usually take the form of a pass-through connector which attaches to a PC parallel port or Mac ADB port. Software can check for the presence of the dongle on the relevant port and, if the dongle is not present, refuse to run.
The simplest dongles consist of a series of wires which connect the port’s data lines in a particular configuration. Others contain an EPROM which can be read by the software or use diodes to block voltages in a specific pattern. All are designed to allow other peripherals to be connected to them without interfering with the connection between the peripheral and the port.
An engineer by the name of Dan Maxwell is credited as being the first person to develop the hardware security device now known as a dongle. His original device, known as a key, was developed at Data General in the early 1970’s but he later started his own company, Data Security, which today markets dongles under the name “SecuriKey”.