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#### 9.16.16 AMD64 ISA vs. Intel64 ISA

There are some discrepancies between AMD64 and Intel64 ISAs.

- For ‘`movsxd`’ with 16-bit destination register, AMD64 supports 32-bit source operand and Intel64 supports 16-bit source operand.
- For far branches (with explicit memory operand), both ISAs support 32- and 16-bit operand size. Intel64 additionally supports 64-bit operand size, encoded as ‘`ljmpq`’ and ‘`lcallq`’ in AT&T syntax and with an explicit ‘`tbyte ptr`’ operand size specifier in Intel syntax.
- ‘`lfs`’, ‘`lgs`’, and ‘`lss`’ similarly allow for 16- and 32-bit operand size (32- and 48-bit memory operand) in both ISAs, while Intel64 additionally supports 64-bit operand sise (80-bit memory operands).