[[File:Atari XE Games System-gen1.jpeg|thumb|right|Atari XEGS]]
The [[Atari 8-bit]] computer series, launched in 1979 as the Atari Home Computer System, included the Atari 400 and 800. Powered by the 8-bit MOS Technology [[6502 ]] CPU and custom coprocessors, these computers offered advanced graphics and sound for their time.
The Atari 800 was the high-end model, while the 400 was a budget-friendly option with a membrane keyboard and 8 KB of RAM. Both supported plug-and-play peripherals via the Atari SIO (Serial I/O) bus, a precursor to USB technology. The architecture was later used in the 1982 Atari 5200 console, though the systems were not software-compatible.
==Hardware==
The 400/800 originally used the standard 6502B CPU. Later 400/800 CPU board was released that boards used the SALLY 6502C (the C is for custom, not CMOS) chip. The SALLY chip equipped all new Atari 400 & 800, and their successors.
In addition to its 1POKEY (POt KEYboard integrated circuit) is a digital Input/Output chip.79 Mhz [[MOS 6502|6502]] CPU, It handles such disparate tasks as the Atari computer offloads some of the work to SIO bus and its specialized chips: ANTICperipherals, CTIA & POKEYaudio generation, keyboard scan, and random number generation. It also digitizes the resistive paddle inputs and controls maskable interrupt (IRQ) requests from peripherals.
ANTIC and CTIA together produce the graphics, up to a resolution of 320x192 pixels, sprites, scrolling in any direction, different graphic modes that can be mixed on the same screen, etc.
When launched in the US, the Atari 400 & 800 came with a CTIA (Color Television Interface Adapter) chip, which offered 9 graphic and text modes (GR.0-8) in Atari BASIC and a 128-colour palette. In early 1982, CTIA was replaced by GTIA (Graphic Television Interface Adapter), which provided 3 additional graphics modes (GR.9-10-11) in Atari BASIC, with a 256-colour palette. The GTIA chip equipped all new Atari 400 & 800, and their successors.
POKEY (POt KEYboard integrated circuit) is a digital Input/Output chip{| class="wikitable"! Parameter !! PAL Atari 8-bit !! NTSC Atari 8-bit|-| Master Clock Frequency || 17. It handles such disparate tasks as the SIO bus and its peripherals734475 MHz || 14.31818 MHz|-| Clock Divider|| 10 || 8|-| CPU Clock Speed || 1, audio generation773, keyboard scan447 Hz || 1, and random number generation789,772 Hz|-| Raster Lines per Frame || 312 || 262|-| CPU Cycles per Line || 114 || 114|-| Total CPU Cycles per Frame || 35,568 || 29,868|-| Calculated Frame Rate || ~49. It also digitizes the resistive paddle inputs and controls maskable interrupt 86 Hz <br /><small>(IRQ1,773,447 / 35,568) requests from peripherals</small> || ~59.92 Hz <br /><small>(1,789,772 / 29,868)</small>|}
==Links==