By default yes, though I worked on a codebase which was ported from M68k to SPARC which had a lot of misaligned memory access. You could opt into having "packed" structs with #pragma pack and avoid the runtime error by compiling all the code with --misalign.

As I recall, this had a performance penalty since memory reads/writes are now byte-by-byte. Also it could make code which assumed atomic reads/writes of 32 bit quantities go awry.