2. Encoding The Opcodes

• Suppose we decided to design a brand-new CPU with a set of 7-bit opcodes.

  • With an opcode of this size we could encode 2⁷ = 128 different instructions.

  • Decoding individual instructions requires a 7-line to 128-line decoder - an expensive piece of circuitry.

• If you have 128 truly unique instructions, there's little you can do other than to decode each instruction individually.

• However, assuming our instructions contain certain patterns, we could reduce the hardware cost by replacing this large decoder with a few smaller decoders.