Amiga Advanced Graphics Architecture

Amiga Advanced Graphics Architecture

Advanced Graphics Architecture (AGA) is the third generation Amiga graphic chip set, first used in the Amiga 4000 in 1992. AGA was codenamed the Pandora chipset by Commodore International internally.

AGA was originally called AA for Advanced Architecture in the United States. The name was later changed to AGA for the European market to reflect that it largely improved the graphical subsystem, and to avoid trademark issues.

AGA is able to display graphics modes with a depth of up to 8 bit per pixel. This allows for 256 colors in indexed display modes and 262144 colors (18-bit) in HAM-8 (Hold-And-Modify) modes. The palette for the AGA chipset has 256 entries from 16777216 colors (24-bit), whereas previous chip sets (OCS and ECS) only allowed 32 colors out of 4096 (64 colors in EHB mode). Other features added to AGA over ECS were super hires smooth scrolling and 32-bit fast page memory fetches to supply the graphics data bandwidth for 8 bitplane graphics modes and wider sprites.

AGA was an incremental upgrade, rather than the dramatic upgrade of the other chipset that Commodore had begun in 1988, AAA, lacking many features that would have made it competitive with other graphic chip sets of its time. Apart from the graphics data fetches, AGA 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 is a speed impediment to graphics operations not tailored for planar modes. In practice, the AGA HAM (Hold-And-Modify) mode is mainly useful in painting programs, picture viewers and for video playback. Workbench in 256 colors is much slower than ECS operation modes for normal application use, a workaround is to use multiple screens with different color depths. AGA also lacks flicker free higher resolution modes, being only able to display 640x480 at 72Hz flicker-free operation. 800x600 mode is rarely used as it could only operate at a flickering 60Hz interlaced mode. In contrast, higher-end PC systems of this era could operate 1024x768 at 72Hz with a full 256-color display. AGA's highest resolution is 1440x580 (262144 colors) in interlaced 50Hz PAL mode, when overscan was used.

These missed opportunities in the AGA upgrade contributed to the Amiga ultimately losing technical leadership in the multimedia area. AGA was to be succeeded by the Hombre chipset, after the long delayed AAA was finally shelved, which was ultimately cancelled due to Commodore's bankruptcy.

AGA was used in the CD32, Amiga 1200 and Amiga 4000.