AGA Chipset — A1200 / A4000 / CD32

Overview

The Advanced Graphics Architecture (AGA) is the final custom chipset developed by Commodore, shipping from 1992. It dramatically expands color depth, palette size, sprite capabilities, and blitter bandwidth while retaining full OCS/ECS backward compatibility.

Chip Summary

Chip	Name	Changes from ECS
Alice	MOS 8374	Super Agnus successor: 64-bit bus, FMODE register
Lisa	(unnamed MOS)	ECS Denise successor: 8-bit palette, 256 colors
Paula	MOS 8364	Unchanged from OCS/ECS

File	Topic
chipset_aga.md	Alice and Lisa internals, AGA architecture
aga_registers_delta.md	New/changed registers vs ECS
aga_palette.md	24-bit color system, 256 registers
aga_display_modes.md	HAM8, 256-color, doublescan, VGA
aga_blitter.md	64-bit blitter bus, FMODE
aga_sprites.md	AGA sprite enhancements: 32/64px width, FMODE, color bank selection (ESPRM/OSPRM)
aga_copper.md	AGA Copper programming guide
cpu_030_040.md	68030/040/060: accelerator catalog, benchmarks, named antipatterns (cache/DMA coherency, missing libraries, timing loops, chip bus speed), FPGA impact, FAQ
akiko_cd32.md	CD32 Akiko chip: C2P conversion, CD-ROM, NVRAM
Gayle IDE & PCMCIA	A1200 Gayle: IDE and PCMCIA (shared with A600)

AGA vs ECS — Key Differences

Feature	ECS	AGA
Color registers	32 (12-bit)	256 (24-bit)
Max simultaneous colors	64 EHB / HAM	256 (or HAM8: 262,144)
Blitter bus	16-bit	64-bit (FMODE)
Sprite width	16 px	64 px
Sprite colors	3+transparent	15+transparent (64-color attached)
Bitplane depth	6 planes max	8 planes
Palette select	1 bank	4 bitplane banks, 4 sprite banks

Identifying AGA at Runtime

#include <graphics/gfxbase.h>

extern struct GfxBase *GfxBase;

BOOL is_aga = (GfxBase->ChipRevBits0 & (1 << GFXB_AA_ALICE)) != 0;

ChipRevBits0 bit	Flag	Meaning
4	`GFXB_AA_ALICE`	AGA Alice present
5	`GFXB_AA_LISA`	AGA Lisa present

AGA Machines — Per-Model Details

Model	CPU	Notes
A1200	68EC020 14 MHz	Budget AGA; Gayle IDE; PCMCIA; 2 MB Chip
A4000	68030/040 25 MHz	High-end; Zorro III; IDE; 2 MB Chip + Fast
A4000T	68040/060	Tower variant; SCSI
CD32	68EC020 14 MHz	Game console; Akiko C2P; CD-ROM; no keyboard

CD32 (1993) — AGA Game Console

The CD32 uses the identical AGA chipset (Alice + Lisa + Paula) as the A1200, but adds the Akiko custom chip — a unique ASIC providing:

Chunky-to-Planar (C2P) hardware conversion — converts 8-bit linear pixel data to planar bitplane format
CD-ROM controller — drives the internal double-speed CD-ROM via PIO (no SCSI, no IDE)
NVRAM interface — I²C controller for 128-byte onboard EEPROM

The CD32 has no Gayle chip — Akiko replaces all storage functions. It has no keyboard, no floppy, no Zorro slots, and no PCMCIA. The only expansion path is the rear port (SX-1/SX-32 add-on units) or the FMV module slot.

See the dedicated article: Akiko — CD32 Custom Chip

A4000T (1994) — Tower Workstation

The A4000T is the tower variant of the A4000 desktop, adding:

Feature	A4000 Desktop	A4000T Tower
CPU	68030 @ 25 MHz or 68040 @ 25 MHz	68040 @ 25 MHz or 68060 @ 50 MHz
SCSI	None	NCR53C710 (Fast SCSI-2, bus-mastering DMA)
Drive bays	1× 3.5" IDE	3× 5.25" + 1× 3.5"
Zorro III	4 slots	5 slots
CPU slot	Yes	Yes (enhanced pinout)
Power supply	Internal 150W	Internal 300W
IDE	On-board (Gayle-less)	On-board + SCSI

The A4000T's NCR53C710 SCSI controller is a high-performance bus-mastering DMA controller — significantly faster than the WD33C93 used in the A3000 and CDTV. It supports up to 7 SCSI devices on an internal 50-pin ribbon cable.

Note

The A4000T was the last Amiga produced by Commodore before the company's bankruptcy in April 1994. Very few units were manufactured, making it one of the rarest stock Amiga models.

References

ADCD 2.1 Hardware Manual — AGA chapters
NDK39: graphics/gfxbase.h, hardware/custom.h
Commodore A1200/A4000 Technical Reference Manuals (local archive)

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