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Graphics modes list 

GR. Mode   Number of colors   Resolution   Memory (bytes)   Display mode
   0              2              40 x 24         992           Text mode
   1              5              20 x 24         672           Text mode
   2              5              20 x 12         420           Text mode
   3              4              40 x 24         432       Graphics mode
   4              2              80 x 48         696       Graphics mode
   5              4              80 x 48        1176       Graphics mode
   6              2             160 x 96        2184       Graphics mode
   7              4             160 x 96        8138       Graphics mode
   8              2            320 x 192        8138       Graphics mode
   9             16             80 x 192        8138       Graphics mode
  10              9             80 x 192        8138       Graphics mode
  11             16             80 x 192        8138       Graphics mode
  12              5              40 x 24        1152           Text mode
  13              5              40 x 12         660           Text mode
  14              2            160 x 192        4296       Graphics mode
  15              4            160 x 192        8138       Graphics mode
Graphics mode 0 (text mode)

Number of colors: 2
Resolution: 40 x 24
Memory (in bytes): 992

Graphics mode 1 (text mode)

Number of colors: 5
Resolution: 20 x 12 (-2)
Memory (in bytes): 672

Graphics mode 2 (text mode)

Number of colors: 5
Resolution: 20 x 24 (-4)
Memory (in bytes): 420

Graphics mode 3 (graphics mode)

Number of colors: 4
Resolution: 40 x 24(-4)
Memory (in bytes): 432

Graphics mode 4 (graphics mode)

Number of colors: 2
Resolution: 80 x 48(-4)
Memory (in bytes): 696

Graphics mode 5 (graphics mode)

Number of colors: 4
Resolution: 80 x 48(-4)
Memory (in bytes): 1176

Graphics mode 6 (graphics mode)

Number of colors: 2
Resolution: 160 x 96(-4)
Memory (in bytes): 2184

Graphics mode 7 (graphics mode)

Number of colors: 4
Resolution: 160 x 96(-4)
Memory (in bytes): 8138

Graphics mode 8 (graphics mode)

Number of colors: 2
Resolution: 320 x 192(-4)
Memory (in bytes): 8138

Graphics mode 9 (graphics mode)

Number of colors: 16
Resolution: 80 x 192
Memory (in bytes): 8138

Graphics mode 10 (graphics mode)

Number of colors: 9
Resolution: 80 x 192
Memory (in bytes): 8138

Graphics mode 11 (graphics mode)

Number of colors: 16
Resolution: 80 x 192
Memory (in bytes): 8138

Graphics mode 12 (text mode)

Number of colors: 5
Resolution: 40 x 24(-4)
Memory (in bytes): 1152

Graphics mode 13 (text mode)

Number of colors: 5
Resolution: 40 x 12(-4)
Memory (in bytes): 660

Graphics mode 14 (graphics mode)

Number of colors: 2
Resolution: 160 x 192(-4)
Memory (in bytes): 4296

Graphics mode 15 (graphics mode)

Number of colors: 4
Resolution: 160 x 192(-4)
Memory (in bytes): 8138

GTIA graphics mode 9 picture taken from Compute!'s Second Book of Atari Graphics

ANTIC

ANTIC ("Alpha-Numeric Television Interface Circuit") is a microprocessor dedicated to the television display. 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. 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 GTIA.

CTIA / GTIA

CTIA ("Color Television Interface Adapter") / GTIA ("George's Television Interface Adapter") is a television interface chip. ANTIC directly controls most of GTIA's operations, but the 6502 can be programmed to intercede and control some or all of GTIA's functions. GTIA converts the digital commands from ANTIC (or the 6502) into the signal that goes to the television. GTIA also adds some factors of its own, such as color values, player-missile graphics, and collision detection. Early 400/800 models included CTIA, later 400/800 models and all later 8-bit Ataris included GTIA. In BASIC, type POKE 623,64 [RETURN] and if the screen blackens, you have the GTIA chip. If it stays blue, you have the old CTIA chip. By the way, apparently no CTIA-equipped Ataris were shipped to Europe.