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Top Document: Atari 8-Bit Computers: Frequently Asked Questions
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1.3) What are the some of the performance features of the 8-bit Atari?

Some of this text by mailto:kendrick@zippy.sonoma.edu (Bill Kendrick).

CLOCK SPEED:
NTSC machines: 1.78979 MHz
PAL machines: 1.773447 MHz

SCREEN REFRESH RATE:
      60 times per second (Hz) on NTSC Ataris
      49.86 Hz on PAL machines

ANTIC AND THE DISPLAY LIST:
ANTIC     CIO/BASIC     Display     Resolution        Number of
Mode #    Graphics #    Type        (full screen)     Colors
---------------------------------------------------------------
  2          0          Char         40 x 24            1 *
  3          -          Char         40 x 19            1 *
  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           1 *
  F          9 +        Map          80 x 192           1 **
  F         10 +        Map          80 x 192           9
  F         11 +        Map          80 x 192           16 ***
  * 1 Hue; 2 Luminances
 ** 1 Hue; 16 Luminances
*** 16 Hues; 1 Luminance
  + require the GTIA chip.  1979-1981 400/800's shipped with CTIA
 ++ Not available via the BASIC GRAPHICS command in 400/800's.

GRAPHICS INDIRECTION (COLOR REGISTERS AND CHARACTER SETS):
Nine color registers are available.  Each color register holds any of 16
luminances x 16 hues = 256 colors.  (Four registers are for player-missile
graphics.

Character sets of 128 8x8 characters, each with a normal and an inverse video
incarnation, are totally redefinable.

PLAYER-MISSLE GRAPHICS:
  Four 8-bit wide, 128 or 256 byte high single color players, and four
    2-bit wide, 128 or 256 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 XOR 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 INTERRUPTS (DLI's):
  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:

  All other screen attributes (color, player/missile horizontal position,
    screen width, player/missile/playfield priority, etc.) can be ajusted
    at any point down the screen via DLI's.

SCROLLING:
  Fine scrolling (both vertical and horizontal) can be enabled on any
    line on the screen.

SOUND:
  Four voices of 8-bit pitch-resolution, 4-bit volume-resolution,
    8-distortion sound can be produced.  2 voices (1 and 2, and/or 3 and 4)
    can be combined to make 16-bit pitch-resolution.  Also 4-bit volume-only
    modes can be enabled for digitally sampled sound replay.

  A fifth "voice" is produced by the internal speaker on Atari 400/800's
    (for keyclick and buzzer) and in the XL's and XE's this was
    (fortunately!) rerouted through the normal audio output, and the
    keyclick can be disabled.