While popular among 'power users', this exposure of a technical implementation detail was against the grain of the Mac user philosophy. Sometimes this value wasn't enough for particular kinds of work, so the value setting had to be exposed to the user to allow them to tweak the heap size to suit their own requirements. The amount of actual RAM allocated to each heap was set by a value coded into the metadata of each application, set by the programmer. Because Apple was now committed to its memory management model, as well as compatibility with existing applications, it was forced to adopt a scheme where each application was allocated its own heap from the available RAM. This was a necessary step forward for users, who found the one-app-at-a-time approach very limiting. The situation worsened with the advent of Switcher, which was a way for a Mac with 512KB or more of memory to run multiple applications at once. Since the entire application heap was dissolved when the application quit, fragmentation was minimized. As long as only one application at a time was run, the system worked well.

The machine itself implemented two areas in memory available for this scheme - the system heap (used for the OS), and the application heap.

If a memory request required compaction of memory, this was done and the table, called the master pointer block, was updated. Apple's scheme was simple - a handle was simply a pointer into a (non relocatable) table of further pointers, which in turn pointed to the data. To solve this, Apple engineers used the concept of a relocatable handle, a reference to memory which allowed the actual data referred to be moved without invalidating the handle. The primary concern of the original engineers appears to have been fragmentation - that is, the repeated allocation and deallocation of memory through pointers leading to many small isolated areas of memory which cannot be used because they are too small, even though the total free memory may be sufficient to satisfy a particular request for memory.

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