12. Selecting Instruction Set

• Keep in mind that it's much easier to add an instruction later than to remove it.

• For starters, it's better to stick with simpler design rather than a more complex one.

• First step: let's choose some generic instruction types for a brand-new CPU.

• For example, most processors will have instructions like the following:

  • Data movement instructions (e.g., MOV)

  • Arithmetic and logical instructions (e.g., ADD, SUB, AND, OR, NOT)

  • Comparison instruction, CMP

  • A set of conditional jump instructions JE, JNE, etc., generally used after the compare instructions.

  • Input/Output instructions GET and PUT.

• The bottom line: allow programmers to efficiently write programs using as few instructions as possible.