Amiga 500
Chip RAM
#### Chip RAM

The stock 512 KB Chip RAM can be complemented by 512 KB using a "trapdoor" expansion (Commodore A501 or compatible). While that expansion memory is connected to the chip bus, hardware limitations of early stock Agnus chip revisions prevent its use as Chip RAM, only the CPU can access it. Suffering from the same contention limitations as Chip RAM, that memory is known as "Slow RAM" or "Pseudo\-fast RAM". Agnus revisions shipped with late A500 are [ECS](/wiki/Amiga_Enhanced_Chip_Set "Amiga Enhanced Chip Set") and allow use of trapdoor RAM as real Chip RAM for a total 1 MB. 

Additionally, several third\-party expansions exist with up to 2 MB on the trapdoor board. Using a [Gary](/wiki/Amiga_custom_chips%23Gary "Amiga custom chips#Gary") adapter, that memory will be mapped as either split on Chip RAM and Slow RAM or fully as Slow RAM, depending on configuration.

Furthermore, using an [A3000](/wiki/Amiga_3000 "Amiga 3000") Agnus on an adapter board, it is possible to expand the Chip RAM to 2 MB, matching the A500\+.


Which Agnus revisions allow use of trapdoor RAM as real Chip RAM for a total 1 MB?