Amiga Advanced Graphics Architecture: Difference between revisions

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'''Amiga 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]].

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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, as well as resulting in ghost artifacts during the common productivity task of [[scrolling]]. 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 couldcan only operate at a flickering {{nowrap|60 Hz}} interlaced mode. In contrast, higher-end PC systems of this era couldcan 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 wasis used.

These missed opportunities in the AGA upgrade contributed to the [[Amiga]] ultimately losing technical leadership in the [[multimedia]] area. After the long delayed AAA was finally shelvedsuspended, AGA was to be succeeded by the [[Hombre chipset]], but this was ultimately cancelled due to Commodore's [[bankruptcy]].

AGA wasis usedpresent in the [[Amiga CD32|CD32]], [[Amiga 1200]] and [[Amiga 4000]].

== Technical details ==

In order to increase memory bandwidth, the [[Chip RAM]] data bus was extended to 32-bit width (as in the [[Amiga 3000|A3000]]<ref>Unlike (unlike AGA, the A3000's Chip RAM is 32-bit for CPU access only.</ref>) and the Alice chip (replacing [[Original Chip Set|OCS]]/[[Amiga Enhanced Chip Set|ECS]] [[MOS Technology Agnus|Agnus]]) was improved to be able to support full width access for bitplane DMA. Additionally, the memory clock was doubled.

Lisa (replacing former [[Original Chip Set#Denise|Denise]]) addedadds support for 8-bit bitplane data fetches, 256 instances of 24-bit palette registers, and for 32-bit data transfer for bitplane graphic and [[Sprite (computer graphics)|sprites]].

The rest of the chipset remainedremains unchanged, as did the Blitter and Copper coprocessors in Alice, still working on 16-bit data.

== See also ==