Modular synthesizers, the first synthesizers, used cables to patch the different sound modules together. Since these machines had no memory to save settings, musicians wrote down the locations of the patch cables and knob positions on a patch sheet (which usually showed a diagram of the synthesizer). After this, an overall sound setting for any type of synthesizer has been known as a patch.
Modern synthesizers can import or export patches via MIDI SYSEX commands. When a synthesizer patch is uploaded to a personal computer which has patch editing software installed, the user can alter the parameters of the patch and download it back to the synthesizer. In many cases the patch editing software on the computer has a better user interface than what is available using the synthesizer's controls alone.
Because there is no standard patch language, it is rare that a patch generated on one synthesizer can be used on a different model synthesizer. However sometimes manufactures will design a family of synthesizers to be compatible. For instance, patches created on the Alesis ION can be used on the Alesis Micron.