AGA stands for
Advanced Graphics Architecture, which is an update of the
OCS and
ECS chipsets in the
Amiga line of computers. AGA offered a full
24-bit palette (compared with 12-bit originally), a new
HAM8 mode, and larger
sprites.
Dual playfield mode was also extended to support 16 colours per
playfield.
Unfortunately, to maintain backwards compatibility, AGA was quite a large hack. For example, originally there were 32 colour registers, so to get a full 256 colour palette bank switching was added. Worse still, since the registers were originally only 13 bits wide, another bit is used to select MSB or LSB.
AGA allowed for greater control over DMA fetching of video memory when building the display, which allowed for larger sprites and more varied display modes. In particular, VGA output at 31kHz was possible.
AGA was used in the Commodore Amiga 1200 and Amiga 4000 computers. A few very rare Amiga 3000s also had AGA. Originally, the plan was to move to the AAA architecture which would have been a complete re-design of the system. Unfortunatley, management killed it only a few months before it would have been ready for production.