One difference is that the Mac OS itself was not initially 32-bit clean, with the top byte being used by the Memory Manager.
replyAh yes, these 68000 pointers have a spare 8 bits for me to use! Because nothing will ever need more than 16 MB of memory. Sigh.
replyIt's all good if you have 128kb ram but they should have had a plan to escape it from day one.
replyThis is how pointer authentication codes work on Arm64.
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