Note that this was a problem on the classic Mac OS (https://en.wikipedia.org/wiki/Classic_Mac_OS_memory_management#32-bit_clean https://en.wikipedia.org/wiki/Cl

Note that this was a problem on the classic Mac OS (https://en.wikipedia.org/wiki/Classic_Mac_OS_memory_management#32-bit_clean https://en.wikipedia.org/wiki/Classic_Mac_OS_memory_manageme..., upper bits of pointers were used as flags) and early ARM processors (https://en.wikipedia.org/wiki/26-bit_computing#Early_ARM_processors https://en.wikipedia.org/wiki/26-bit_computing#Early_ARM_pro..., combined program status register and program counter resulting in an effectively 26-bit system). Neither of these systems had an MMU, thus causing the breakage you mention. On a modern system with an MMU, one could instead reduce the size of a process' address space in exchange for tag bits.