The Atari ST is a line of home computers from Atari Corporation and the successor to the Atari 8-bit family. The initial ST model, the 520ST, saw limited release in April–June 1985 and was widely available in July. which refers to the Motorola 68000's 16-bit external bus and 32-bit internals. The hardware was so similar to Apple's Macintosh at the time that with the addition of the Spectre GCR the ST was able to run Macintosh software faster than an actual Mac Plus at the time (since the Atari's clock speed was higher) and with a larger and higher resolution display. In fact, the Stacy (the laptop version of the Atari ST) was the first and only way to own a laptop running Mac OS at the time since Apple did not offer one until much later. The ST was sold with either Atari's color monitor or the less expensive monochrome monitor. The system's two color graphics modes are only available on the former while the highest-resolution mode needs the monochrome monitor. In some markets, particularly Germany, the machine gained a strong foothold as a small business machine for CAD and desktop publishing work. Thanks to its built-in MIDI ports, the ST enjoyed success for running music sequencer software and as a controller of musical instruments among amateurs and well-known musicians alike. The ST was superseded by the Atari STE, Atari TT, Atari MEGA STE, and Falcon computers.