| ADDRESS | FUNCTION | SIZE |
| 0000 1FFF |
RAM initially supplied in the product |
8K |
| 2000 7FFF |
RAM Expansion * |
|
| 8000 BFFF |
ROM Cartridge. (Colleen left and right slot and Candy single slot all address to this space) |
16K |
| C000 CFFF |
Reserved for future OS expansion | 4K |
| D000 D7FF |
Hardware addresses |
2K |
| D800 FFFF |
Operating system and Maths routines |
10K |
* RAM expansion can actually extend to BFFF.
However, the ROM cartridges will deselect the RAM.
Deselection occurs on 8K boundaries.
Atari 400 units are RAM expandable only at the factory.
They can accept RAM up to 2FFF (16K) when fully extended.