Amiga Advanced Graphics Architecture — AGA — is the third-generation Amiga graphics chipset, first used in the Amiga 4000 in 1992. Before release, AGA was known by the codename Pandora at Commodore.

The AGA chipset was initially called AA for the American market introduction. The name was later changed to AGA for the European market to indicate the greatly improved graphics subsystem and to avoid trademark issues.

Amiga Advanced Graphics is capable of display modes with up to 8 bits per pixel. This allows 256 colors in indexed display modes and 262,144 colors (18-bit) in Hold-and-Modify (HAM-8) modes. The AGA palette has 256 entries from 16,777,216 colors (24-bit), while previous chipsets — OCS and ECS — only allowed 32 colors from 4096, or 64 colors in EHB mode. This advancement was made possible by the Paula, Agnus, and Denise chips and their successors.

Other features added to AGA over ECS include super-resolution smooth scrolling and 32-bit fast page memory fetch to supply graphics data bandwidth for 8 bitplane graphics modes and wider sprites.

An Upgrade That Could Have Been More

The AGA chipset is a slow and low-impact upgrade instead of the dramatic upgrade of another chipset Commodore had begun in 1988 — the Amiga Advanced Architecture (AAA). AGA lacks many features that could have made it competitive with other graphics chipsets of its time.

Apart from graphics data fetch, AGA still operates only on 16-bit data — meaning significant bandwidth is wasted during register accesses and Copper and Blitter operations. The lack of a chunky graphics mode is a hindrance to graphics operations not designed for planar modes, leading to sprite artifacts during common scrolling operations.

In practice, AGA HAM mode is mainly useful in paint programs, picture viewers, and for video playback. Workbench in 256 colors is much slower than ECS modes for normal application use. The solution is to use multiple screens with different color depths.

AGA lacks higher-resolution non-flickering modes, as it can only display 640×480 in flicker-free 72Hz operation. The 800×600 mode is rarely used as it can only operate in 60Hz interlaced flicker. In contrast, more advanced PC systems of this period could operate at 1024×768 at 72Hz with full 256-color display. AGA's highest resolution can display 1440×580 (262,144 colors) in PAL 50Hz interlaced when overscan is used.

These missed opportunities in AGA's upgrade eventually caused the Amiga to lose its technical leadership in multimedia. After AAA was finally suspended after long delays, the Hombre chipset was supposed to succeed AGA, but it was ultimately canceled due to Commodore's bankruptcy.

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

Technical Details

To increase memory bandwidth, the chip RAM data bus was widened to 32 bits like the Amiga 3000 — unlike AGA, the Amiga 3000's chip RAM is only 32-bit for processor access — and the Alice chip (replacing OCS/ECS Agnus) was improved to support full-width access for bitplane DMA. Bandwidth was doubled again using Fast Page Mode RAM.

Lisa (replacing Denise) adds support for 8-bit bitplane data fetch, 256 entries of 24-bit palette registers, and 32-bit data transfers for bitplane graphics and sprites. The rest of the chipset remains unchanged — the Blitter and Copper processors in Alice still operate on 16-bit data.