Beating a dead horse (wish I knew how to tie in the graphic, grin).
The early Amigas (1000, 500, 2000, 600, & CDTV) were all designed with 16-bit data bus on the motherboard. Memory that could be shared by the custom chips AND CPU was addressed and refreshed by the Agnus chip. The Agnus was the traffic cop, the chip with the most authority on the motherboard. Shared memory was called Chip memory.
Memory that the 68000 CPU did not have to share or wait for was called Fast memory. Fast memory expansion boards were normally added on and had their own refresh circuitry. Amigas with CPUs that could only interface thru 16-bit data buses could be expanded with a maximum of 8 megabytes of fast ram. This was also the Zorro II adress limit.
SLOW memory was a wierd category that Commodore should never have allowed. It is trap door memory on the original A500 (not the + model), the board was called the A501. It was mapped outside of Chip memory space to be compatible with the earliest Agnus chips (OCS, which only allowed 512K of Chip). It was still refreshed by the Agnus, so the CPU had to wait it's turn to use it just like true Chip memory. Also, the other custom chips could not share it. It is the worst kind of memory expansion. Confusingly, Workbench called this memory "Fast" on the title bar, even though it was neither true Fast nor true Chip memory. There is a motherboard hack for A500s (not the + model) that allows a user to re-map the A501 to the true Chip memory space if the motherboard has a 1 Meg Agnus (ECS). Many of us have done this.
32-bit memory came into being with the first full 32-bit accelerators (68020s, 030s, 040s, and 060s). This memory was mapped outside the Zorro II range and was fitted directly onto the accelerator. It is technically a kind of Fast memory because the CPU does not have to share it.
The 3000, 4000, 1200, and CD-32 all had the full 32-bit data bus and CPU on the motherboard. This is part of the Zorro III specification.
The A500+, A600, 1200, 3000, 4000, and CD-32 all shipped with the latest and greatest 2 Meg Agnus chips (ECS). No motherboard re-mapping required!
The 1000, early 500s and 2000s had the Original Chip Set (OCS). Later 500s, 2000s, 600s, 3000s, and CDTVs had the Enhansed Chip Set (ECS). ECS Agnus was defined as both the 1 Meg and 2 Meg versions, I think. The 1200, 4000 and CD-32 had improved custom chips called AGA (better graphics). A version of the ECS Agnus was used in AGA machines.
Sorry for the long windedness!
