'Virtual' instruments within software sequencers or 'DAWs' (Digital Audio Workstations) have now become the standard instrumentation for anyone writing music with computers. There are many plug-ins that offer direct emulations of original hardware such as Native Instruments' Pro 53 (Sequential Circuits Prophet V) and FM7 (Yamaha's DX7), and Arturia's CS80 (Yamaha CS-80) and ARP 2600. These are often of such good quality that it is virtually impossible to distinguish the original from the pretender! Other plug-ins feature original user interfaces, and use a variety of the synthesis methods we have discussed here. Software sequencers often come with excellent software synthesizers built-in, such as Logic's ES2 and Sculpture. A big advantage of plug-ins is that they completely integrate with their software host, so that all settings, such as which instruments you have on each track and what patches are used, can be saved with your song.