resolution: 640 × 200 (4 color), palette of 512 colors High resolution: 640 × 400, monochrome Sound: Yamaha YM2149 3-voice squarewave plus 1-voice white noise mono Programmable Sound Generator Drive: Single-sided 3" floppy disk drive, 360 KB capacity when formatted to standard 9 sector, 80 track layout. Ports: TV out (on ST-M and ST-FM models, NTSC or PAL standard RF modulated), MIDI in/out (with 'out-thru'), RS-232 serial, Centronics parallel (printer), monitor (RGB or Composite Video color and mono, 13-pin DIN), extra disk drive port (14-pin DIN), DMA port (ACSI port, Atari Computer System Interface) for hard disks and Atari Laser Printer (sharing RAM with computer system), joystick and mouse ports (9-pin MSX standard) Operating System: TOS v1.00 (TOS meaning The Operating System) with the Graphics Environment Manager (GEM) Very early machines have the OS on a floppy disk before a final version was burned into ROM. This version of TOS was bootstrapped from a small core boot ROM. In 1986, most production models became STFs, with an integrated single- (520STF) or double-sided (1040STF) double density floppy disk drive built-in, but no other changes. Also in 1986, the 520STM (or 520STM) added an RF Modulator for allowing the low and medium resolution color modes when connected to a TV. Later F and FM models of the 520 had a built-in double-sided disk drive instead of a single-sided one. STE As originally released in the 520STE/1040STE: All of the features of the 520STFM/1040STFM Extended palette of 4,096 available colors to choose from Blitter chip (stylized as BLiTTER) to copy/fill/clear large data blocks with a max write rate of 4 Mbytes/s Hardware support for horizontal and vertical fine scrolling and split screen (using the Shifter video chip) DMA sound chip with 2-channels stereo 8-bit PCM sound at 6.25/12.5/25/50 kHz and stereo RCA audio-out jacks (using enhancements to the Shifter video chip to support audio shifting) National LMC 1992 audio controller chip, allowing adjustable left/right/master volume and bass and treble EQ via a Microwire interface Memory: 30-pin SIMM memory slots (SIPP packages in earliest versions) allowing upgrades up to 4 MB Allowable memory sizes including only 0.5, 1.0, 2.0, 2.5 and 4.0 MB due to configuration restraints (however, 2.5 MB is not officially supported and has compatibility problems). Later third-party upgrade kits allow a maximum of 14MB w/Magnum-ST, bypassing the stock MMU with a replacement unit and the additional chips on a separate board