1.1) What is an Atari 8-bit computer?

Based in Silicon Valley in the USA, the company known as Atari produced a line of home computers from 1979 to 1992 often referred to collectively as the "Atari 8-bits," the "8-bit Ataris," the "400/800/XL/XE series," etc. The computers included the 400, 800, 1200XL, 600XL, 800XL, 65XE, 130XE, 800XE, and the XE game system. For basic marketplace context, here are the release years of the 8-bit Atari computers alongside release years of significant competing home/personal computers. Note: Market dynamics varied substantially around the world. 1977: Apple II, Commodore PET, Radio Shack TRS-80 1978: ARI Cybervision 2001 1979: Atari 400/800, Apple II Plus, Texas Instruments TI-99/4 1980: Radio Shack TRS-80 Model III, TRS-80 Color Computer, Sinclair ZX80 1981: Acorn BBC Micro, Commodore VIC-20, IBM PC, Osborne 1, Sinclair ZX81, Texas Instruments TI-99/4A 1982: Commodore 64, Kaypro II, Sinclair ZX Spectrum 1983: Atari 1200XL/600XL/800XL, Acorn Electron, Apple IIe, Coleco Adam, MSX, IBM PC XT, Radio Shack TRS-80 Model 4, TRS-80 Color Computer 2 1984: Amstrad CPC, Apple IIc, Apple Macintosh, IBM PCjr, IBM PC AT 1985: Atari 65XE/130XE, Atari 520ST, Commodore 128, Commodore Amiga 1986: Atari 1040ST, Apple Macintosh Plus, Tandy Color Computer 3 1987: Atari 800XE, Acorn Archimedes, Atari Mega ST, Apple Macintosh II, Apple Macintosh SE, Commodore Amiga 500, IBM PS/2 1987 also saw the release of the Atari XE game system, competing alongside Atari's own 7800 (released in 1986) and legacy 2600 (available since 1977) systems, and competing directly against the leading home gaming consoles of the time, the Nintendo Entertainment System and the Sega Master System. In marketing their computers to the public, Atari always had to contend with their company history and reputation as a maker of video games. While the 8-bit Atari computers in their heyday were technically quite comparable if not superior in the worlds of home and business personal computing, they also live up to the name "Atari" with a huge library of video games which were often outstanding for their time. The 8-bit Atari computers do not use the same cartridges or floppy disks as any other Atari platforms, such as the 2600 Video Computer System (VCS), the 5200 SuperSystem, the 7800 ProSystem, or the ST/TT/Falcon computers. All of these but the 5200, however, do share (essentially) the same joystick/ controller hardware port. While the 5200 controller ports are different, the 5200 hardware platform is very closely related the 8-bit Atari computers, including use of the same custom chipset (SALLY/ANTIC/GTIA/POKEY). Differences in the 5200 include a fixed 16KiB of RAM, fixed 32KiB ROM cartridge size, a physically different cartridge port, and a much smaller 2KiB operating system. Here are some of the hardware performance specifications of the 8-bit Atari computers: 6502 MPU: MOS Technology MCS6502A or equivalent (most NTSC 400/800 machines) Atari SALLY (late NTSC 400/800, all PAL 400/800, and all XL/XE) CPU CLOCK RATE: 1.7897725MHz (NTSC machines) 1.7734470MHz (PAL/SECAM machines) FRAME REFRESH RATE: 59.94Hz (NTSC machines) 49.86Hz (PAL/SECAM machines) MACHINE CYCLES per FRAME: 29859 (NTSC machines) (1.7897725MHz / 59.94Hz) 35568 (PAL/SECAM machines) (1.7734470MHz / 49.86Hz) SCAN LINES per FRAME 262 (NTSC machines) 312 (PAL/SECAM machines) MACHINE CYCLES per SCAN LINE 114 (NTSC machines: 29859 cycles/frame / 262 lines/frame; PAL/SECAM machines: 35568 cycles/frame / 312 lines/frame) COLOR CLOCKS per MACHINE CYCLE 2 COLOR CLOCKS per SCAN LINE 228 (2 color clocks/machine cycle * 114 machine cycles/scan line) MAXIMUM SCAN LINE WIDTH = "WIDE PLAYFIELD" 176 color clocks MAXIMUM RESOLUTION = GRAPHICS PIXEL 0.5 color clock MAXIMUM HORIZONTAL FRAME RESOLUTION 352 pixels (176 color clocks / 0.5 color clock) MAXIMUM VERTICAL FRAME RESOLUTION 240 pixels (240 scan lines per frame) GRAPHICS MODES: ANTIC GTIA AtariOS Display Resolution Colors Mode # Mode # Mode # Type (full screen) (Color Registers) ---------------------------------------------------------------------------- 2 0 Char 40 x 24 3 * 3 - Char 40 x 19 3 * 4 12 ++ Char 40 x 24 5 5 13 ++ Char 40 x 12 5 6 1 Char 20 x 24 5 7 2 Char 20 x 12 5 8 3 Map 40 x 24 4 9 4 Map 80 x 48 2 A 5 Map 80 x 48 4 B 6 Map 160 x 96 2 C 14 ++ Map 160 x 192 2 D 7 Map 160 x 96 4 E 15 ++ Map 160 x 192 4 F 8 Map 320 x 192 3 * F 1 + 9 Map 80 x 192 16 or 8 ** F 2 + 10 Map 80 x 192 9 F 3 + 11 Map 80 x 192 16 *** + GTIA Modes require GTIA chip or FGTIA chip (With CTIA these modes are considered valid by the OS but do not work.) ++ Supported by the XL OS (not supported by the 400/800 OS) * 2 of the 3 available color registers share the same color/hue in this mode ** GTIA: 16 luminances of one color/hue FGTIA: 8 luminances of one color/hue *** 16 colors/hues all sharing the same luminance GRAPHICS INDIRECTION (COLOR REGISTERS AND CHARACTER SETS): Nine Color Registers are provided: - Background (used in all graphics modes) - Playfield 0-3 (at least one used in all graphics modes except GTIA 1&3) - Player-Missile 0-3 (used in GTIA Mode 2; Player-Missiles discussed below) Each color register holds both a color/hue setting and a luminance/brightness setting. In most graphics modes, each of the available color registers may hold any one of 16 colors/hues combined with any one of 8 luminance/brightness settings, for a total palette of 128 possible colors. In GTIA Mode 1 only, with the GTIA chip only, the 16 available colors/hues can each be combined with 16 different luminance/brightness settings, for a total palette of 256 possible colors. Character sets of 128 8x8 characters, each with a normal and an inverse video incarnation, are totally redefinable. PLAYER-MISSILE GRAPHICS: The Atari term for "sprites" where a sprite is a graphical video display object handled independendly from the memory bitmap of the video display. Four 8-bit wide, 120 or 240 byte high single color Players, and four 2-bit wide, 120 or 240 byte high single color Missiles are available. A mode to combine the 4 Missiles into a 5th 8-bit wide Player is also available, as is a mode to OR colors or blacken out colors when Players overlap (good for making three colors out of two Players!) Players and Missiles have adjustable priority and collision detection. DISPLAY LIST: Screen modes can be mixed (by lines) down the screen using the Display List - a program which is executed by the ANTIC graphics chip every screen refresh. DISPLAY LIST INTERRUPTS (DLIs): Other screen attributes (color, player/missile horizontal position, screen width, player/missile/playfield priority, etc.) can be adjusted at any point down the screen via DLIs. SCROLLING: Fine scrolling (both vertical and horizontal) can be enabled on any line on the screen. SOUND: Up to 5 distinct sounds can be produced simultaneously: four main voices plus the Console Speaker. Sound output is monaural/monophonic/single channel, except for the 400/800 where Console Speaker sounds are output separately to a speaker inside the computer. The four main voices can be configured in one of the following three ways: - 4 voices, each with one of 256 unique frequencies/pitches - 2 voices, each with one of 65,536 unique frequencies/pitches - 1 voice with one of 65,536 frequencies/pitches and 2 voices with one of 256 frequencies/pitches each Each of the main voices may produce 8 types of tones: pure tones (square wave type), or tones produced with one of 7 types of "noise" which is known as "distortion" on the Atari. Each of the main voices may be produced at one of 16 volumes. Direct control of the position of the speaker cone, known today as pulse- code modulation or PCM, is available at a bit depth of 4 bits, for a volume resolution of 16 possible values (4-bit PCM). This is known as "Volume Control Only" or "Volume Only" sound on the Atari. The Console Speaker was intended only for system keyclick and buzzer, but it may also be programmed as 1-bit PCM. VERTICAL BLANK INTERRUPTS (VBIs): A software routine may be designed to execute as a VBI. There are two varieties of VBI: Immediate and Deferred. An Immediate VBI completes execution within the vertical blank time, which is the time allotted for a CRT display to shut the electron beam off at the lower-right of the display and reposition it back on the top-left of the display to commence drawing of the next frame. A Deferred VBI routine completes execution between the initiation of one vertical blank and the next. Atari 8-bit computers were supplied with the proprietary Atari Operating System contained in Read Only Memory (ROM) as an integral feature of the computer. The Atari OS is described elsewhere in this FAQ List.