It is also compatible with nearly all 8-bit software running on those systems. Like the Apple II+, IIe, and IIc, the IIGS also includes Applesoft BASIC and a machine-language monitor (which can be used for very simple assembly language programming) in ROM, so they can be used even with no operating system loaded from disk. The 8-bit software runs twice as fast unless the user turns down the processor speed in the IIGS control panel. System Software The Apple IIGS System Software utilizes a graphical user interface (GUI) very similar to that of the Macintosh and somewhat like GEM for PCs and the operating systems of contemporary Atari and Amiga computers. Early versions of the System Software are based on the ProDOS 16 operating system, which is based on the original ProDOS operating system for 8-bit Apple II computers. Although it was modified so that 16-bit Apple IIGS software can run on it, ProDOS 16 was written largely in 8-bit code and does not take full advantage of the IIGS's capabilities. Later System Software versions (starting with version 4.0) replaced ProDOS 16 with a new 16-bit operating system known as GS/OS. It better utilizes the unique capabilities of the IIGS and includes many valuable new features. The IIGS System Software was substantially enhanced and expanded over the years during which it was developed, culminating in its final official version, System 6.0.1, which was released in 1993. In July 2015, members of a computer group from France released a new, though unofficial, version of that System Software, dubbed "System 6.0.2" (and later followed by System 6.0.3 and 6.0.4), that primarily fixed some bugs. Graphical user interface Similar to that of the Macintosh, the IIGS System Software provides a mouse-driven graphical user interface using concepts such as windows, menus, and icons. This was implemented by a "toolbox" of code, some of which resides in the computer's ROM and some of which is loaded from disk. Only one major application can run at a time, although other, smaller programs, known as Desk Accessories, can be used simultaneously. The IIGS has a Finder application very similar to the Macintosh's, which allows the user to manipulate files and launch applications. By default, the Finder is displayed when the computer starts up and whenever the user quits an application that is started from it, although the startup application can be changed by the user. Software companies