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Most of processors predating the 8086 had 8-bit opcodes, allowing 256 different instructions.
A two-byte opcode would allow 65,536 different instructions...
...but from a practical standpoint,
most-frequently-used instructions continue to have 8-bit opcodes,
less-frequently-used instructions have two-byte opcodes,
three (or more) byte opcodes are mostly for the rarely-used-instructions.
Such strategy makes a typical program significantly shorter, compared to a uniform two-byte opcode.
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