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22. Encoding Eight, Sixteen, and Thirty-Two Bit Operands

When Intel designed the 8086, one bit in the opcode, s, selected between 8 and 16 bit integer operand sizes.
Later, when CPU added 32-bit integers to its architecture on 80386 chip, there was a problem:
- three encodings were needed to support 8, 16, and 32 bit sizes.
Solution was an operand size prefix byte.

Intel studied x86 instruction set and came to the conclusion:
- in a 32-bit environment, programs were more likely to use 8-bit and 32-bit operands far more often than 16-bit operands.
So Intel decided to let the size bit s in the opcode select between 8- and 32-bit operands.

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