32-bit addressing

32-bit addressing involves computers that can locate memory addresses that are 32-bits (4 bytes) wide, allowing for a theoretical maximum of 4 gigabytes of memory, though logic board and CPU configurations may add other limitations.

The first Macintosh operating system to support 32-bit addressing is System 7, but the first Apple computer with "32-bit clean" ROMs to support it is the Macintosh IIci. Connectix developed Optima and MODE32 to patch the ROMs of older Macintosh II-era models to retroactively add such support and surpass the 8-to-14 megabyte limit of classic Mac OS's previous 24-bit addressing space. Because applications from the 24-bit era that were not "32-bit clean" would crash in a 32-bit system, the Memory control panel in System 7 through 7.5.5 included a toggle switch to enable 24-bit support. However, Quadra AV and Power Macintosh computers, and Mac OS 7.6 do not support 24-bit addressing and only run in 32-bit mode.

32-bit applications under Mac OS X could be allocated up to 3GB of RAM, but Macintosh models in the 2000s soon found this limit to be a bottleneck. The integration of 64-bit processors, such as the PowerPC G5 and Intel Core 2, in newer Macintosh models allowed for memory configurations greater than 4GB.