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Inside Macintosh: Mac OS Runtime Architectures /
Chapter 10 - Classic 68K Runtime Architecture

The A5 World

Every classic 68K application contains an A5 world, an area of memory that stores the following items:

The data is referenced as offsets from the value of the A5 register, hence the name A5 world. The application's global variables and QuickDraw global variables are referenced with negative offsets from A5, while application parameters and jump table entries are referenced with positive offsets.

Figure 10-1 shows a classic 68K A5 world.

Figure 10-1 Classic 68K A5 world

The system global variable CurrentA5 holds the value of the A5 register.

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11 MARCH 1997

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