The Atari STFM was the most popular of Atari's 16-bit micros, available as either the 520STFM with 512KB RAM or the 1040STFM with 1MB. Unlike its predecesors, the STFM contained a built in TV modulator, a 3½" disc drive (initially with a 360k capacity, but increased to 720k on later models) and had both the operating system (TOS) and the graphical user interface (GEM) stored in ROM.