Amiga Advanced Graphics Architecture: Difference between revisions

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'''Advanced Graphics Architecture''' ('''AGA''') is the third generation [[Amiga]] graphic chip set, first used in the [[Amiga 4000]] in 1992. before release AGA was codenamed '''Pandora''' by [[Commodore International]].

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. <ref>[http://www.amigahistory.co.uk/amigaaga.html The Amiga AGA Chipset<!-- Bot generated title -->]</ref>

AGA is able to display graphics modes with a depth of up to {{nowrap|8 bit}} per pixel. This allows for {{nowrap|256 colors}} in indexed display modes and {{nowrap|262 144 colors}} (18-bit) in [[Hold And Modify|HAM]]-8 ([[Hold-And-Modify]]) modes. The palette for the AGA chipset has 256 entries from {{nowrap|16 777 216 colors}} (24-bit), whereas previous chip sets ([[Amiga Original chipset|OCS]] and [[Amiga Enhanced Chip Set|ECS]]) only allowed {{nowrap|32 colors}} out of 4096 (64 colors in [[Amiga Halfbrite mode|EHB mode]]). Other features added to AGA over [[Amiga Enhanced Chip Set|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 (computer graphics)|sprites]].

AGA was an incremental upgrade, rather than the dramatic upgrade of the other chipset that Commodore had begun in 1988, [[AAA chipset|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 [[Amiga Original chipset#Copper|copper]] and [[blitter]] operations. Also the lack of a [[packed pixel|chunky]] graphics mode is a speed impediment to graphics operations not tailored for [[Planar (computer graphics)|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 [[Amiga Enhanced Chip Set|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 {{nowrap|640 × 480}} at {{nowrap|72 Hz}} flicker-free operation. {{nowrap|800 × 600}} mode is rarely used as it could only operate at a flickering {{nowrap|60 Hz}} interlaced mode. In contrast, higher-end PC systems of this era could operate {{nowrap|1024 × 768}} at {{nowrap|72 Hz}} with a full 256-color display. AGA's highest resolution is {{nowrap|1440 × 580}} {{nowrap|(262 144 colors)}} in interlaced {{nowrap|50 Hz}} {{nowrap|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]].