How many bytes per memory access? What is a word?
Word
A word is the processor's "natural" data unit: the size of a general-purpose register and of a pointer. On arm64 (all modern iPhone/iPad/Mac) a word is 8 bytes (64 bits). Hence the sizes: Int and any pointer — 8 bytes, String — 16 bytes (2 words), Array — 8 bytes (pointer to the buffer), an object header — 16 bytes (isa + refcount).
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