Does unaligned memory access always cause bus errors?

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  1. It may be significantly slower to access unaligned memory (as in, several times slower).

  2. Not all platforms even support unaligned access – x86 and x64 do, but ia64 (Itanium) does not, for example.

  3. A compiler can emulate unaligned access (VC++ does that for pointers declared as __unaligned on ia64, for example) – by inserting additional checks to detect the unaligned case, and loading/storing parts of the object that straddle the alignment boundary separately. That is even slower than unaligned access on platforms which natively support it, however.

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