*ANTIC is dedicated to the preparation of the video signal. It is a true microprocessor; it has an instruction set, a program called "the display list", and data. The display list and the display data are written into RAM by the 6502 CPU. ANTIC retrieves this information from RAM using Direct Memory Access (DMA). It processes the higher-level instructions in the display list and translates these instructions into a real-time stream of simple instructions to CTIA.
*CTIA is a television interface chip. ANTIC directly controls most of CTIA's operations, but the 6502 CPU can be programmed to intercede and control some or all of CTIA's functions. CTIA converts the digital commands from ANTIC (or the 6502) into a video signal that goes to the TV set or monitor. CTIA also adds some factors of its own, such as colour values, sprites graphics, and collision detection. Games ordinarily requiring 48 KiB of RAM or more to handle complicated animation can be done in 16 Kib of RAM on machines with sprites (players-missiles in Atari's vocabulary).
When launched in the US, the Atari 400 & 800 came with a CTIA 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, which provided 3 additional graphics modes (GR.9-10-11) in Atari BASIC, with a 256-colour palette. The GTIA chip became standard and equipped all new Atari 400 & 800, as well as all computers that succeeded them: the 1200XL / 600XL / 800XL / 65XE / 130XE / XEgs / 800XE.