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The Amiga's Custom Chips

One of the major differences between the Amiga and all other computers was that the Amiga used custom chips for graphics and sound, and because of this the Amiga was far superior to anything else available at the time, including the Mac. Processing of graphics was considerably faster, with more colours, and the sound was exceptional to say the least. These special chips, unique to the Amiga, had specialised functions that worked independently of the CPU chip, and left the CPU free to get on with other tasks. Whereas the CPU's in PCs and Macs had to stop what they were doing at least 200 times a second to refresh the memory, refresh the screen image, check for keys being pressed, and various other housekeeping tasks etc, the Amiga left these mundane tasks to the custom chips and significantly reduced the loading on the CPU by as much as 50% or more. Each major update of the Amiga has utilised a new set of custom chips which correspond to one of the following:

(ICS) - Initial Chip Set Used in the A1000 and A2000
(OCS) - Original Chip Set Used in the A500, A1500, B2000, A2500 and CDTV
(ECS) - Enhanced Chip Set Used in the A500+, A600, B2000, A2500 and A3000
(AGA) - Advanced Graphics Architecture Used in the A1200, A4000 and CD32
(AAA) - Advanced Amiga Architecture Not used in any production machine
Other Custom Chips Used in various machines
Kickstart Roms Used in all machines

In addition to the Custom Chip Sets, there was another group of chips that were used by the various Amigas which, although not totally unrelated to the Custom Chips, were not normally included in the chip set groupings. These chips are:

Buster A custom chip introduced on the A3000 to perform BUS management, and enhanced for the A4000.
CIA Not really one of the custom chips but an important chip because it acted as a buffer between the Amiga and the outside world - i.e. serial port, parallel port, mouse/joystick ports etc. This chip could easily be damaged by static electricity or voltage changes when connecting and/or disconnecting devices etc (including joysticks and printers) while the power was on. There were two of them in every Amiga - one to handle odd data and another for even data.
Gary The custom chip that provided all BUS control signals, all address decoding and the keyboard reset interface. It also generated the 68000 VPA signal and handled some of the floppy circuitry. This chip was superceded by the GAYLE chip on the A600 and later machines.
Gayle The custom chip that provided all BUS control signals, all address decoding and the keyboard reset interface. It also generated the 68000 VPA signal and handled some of the floppy drive circuitry. This chip replaced the GARY chip used on the A600 and later machines.
Ramsey The name given to the RAM controller chip found in A3000s, etc.


Copyright 2005 Amiga Auckland Inc. All rights reserved.
Revised: September 25, 2005.