As 1111 was reserved for use by co-processors such as the 68881 FPU, Apple chose 1010 (hexadecimal A) as the prefix for operating system calls. Further, they each had their own dedicated interrupt vector, separate from the generic illegal opcode handler. Motorola specified that instructions beginning with 11 would never be used in future 68000 family processors, thus freeing them for use as such by an operating system. The original Motorola 68000 family implementation of the Macintosh operating system executes system calls using that processor's illegal opcode exception handling mechanism. Note that the Toolbox does not draw the menu onscreen: menus were designed to have a customizable appearance, so the drawing code was stored in a resource, which could be on a disk.ġ. The Toolbox consists of subroutines essential enough to be permanently kept in memory and accessible by a two-byte machine instruction however it excludes core "kernel" functionality such as memory management and the file system. As the original Macintosh was designed without virtual memory or memory protection, it was important to classify code according to when it should be loaded into memory or kept on disk, and how it should be accessed. The Toolbox consists of a number of "managers," software components such as QuickDraw, responsible for drawing onscreen graphics, and the Menu Manager, which maintain data structures describing the menu bar. The Macintosh Toolbox implements many of the high-level features of the Classic Mac OS, including a set of application programming interfaces for software development on the platform.
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