Memory Map

In both the low- and high-resolution models, the operating system ROM is in the first 8K of memory space. Cartridge ROM resides in memory between 8K to 16K. Standard screen RAM begins at 16K and occupies 4K bytes.* All memory space above $5000 is available for expansion.

When data is read from a memory location between 0–16K, the data come from ROM. When data is written in a memory location (X) between 0–16K, the system actually writes a modified form of the data in location X+16K. The modification is performed by the “Magic System” in the Data Chip and Address Chip. Thus the memory from 0 to 16K is called “Magic Memory,” and the first 4K ($0–$0FFF) is considered “Magic RAM,” since it is the same size as standard screen RAM.

* The last sixteen bytes of screen RAM ($4FF0–$4FFF) are not visible onscreen, and thus are available for use as scratchpad RAM.

[NM:82–3]