A common way to handle the opcode shortage (one the Intel designers have employed) is to use a prefix opcode byte:
Prefix opcode expansion scheme uses an opcode prefix byte as follows:
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Decode prefix byte in memory.
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Read and decode the next byte in memory as the actual opcode.
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However, the second opcode byte uses a completely different encoding scheme.
Therefore, prefix lets you specify as many new instructions as you can encode in that byte (or bytes, if you prefer).