Advanced Graphics Architecture
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Advanced Graphics Architecture (AGA) was the name used for the improved graphics chipset of the third generation Amiga computers at the beginning of the 1990s (Second generation had ECS). In the United States AGA was originally called AA for Advanced Architecture, whereas in Europe the name was changed to AGA to reflect that it largely improved the graphical subsystem (opposed to the architecture in its entirety), and to avoid trademark issues. [1]
AGA is able to do 8-bit (256 colors) in normal display mode and 262144 colors in Hold-And-Modify (HAM) mode (18-bit color, 6-bit per RGB channel). Palette for AGA chipset is 16777216 colors (24-bit). The original Amiga chipset (OCS) had 4096 colors (12-bit, 4-bit per RGB channel), of which 32 could be displayed unless in half-bright (which provided an additional 32 colors fixed at half the brightness of the first 32) or HAM mode. Other features added to AGA over ECS were superhires smooth scrolling and 32-bit fast page memory fetches to supply the graphics data bandwidth for 8 bitplane graphics modes and wider sprites.
Apart from the graphics data fetches the chipset still operates on 16-bit data only, meaning that a lot of bandwidth is wasted during register accesses and copper and blitter operations. Also the lack of a chunky graphics mode was a speed impediment to graphics operations not tailored for planar modes. Over all the AGA chipset was a basic evolutionary upgrade.
AGA was included in the CD32, Amiga 1200 and Amiga 4000.
See also
es:AGA fr:Architecture graphique avancée pl:AGA fi:AGA (piirisarja) ru:AGA