Computer Architecture and Security by Wang Shuangbao Paul Ledley Robert S

Author:Wang, Shuangbao Paul, Ledley, Robert S.
Language: eng
Format: epub
Publisher: Wiley
Published: 2012-10-18T04:00:00+00:00

6.1.1 Instruction Classifications

Instructions usually contain two components: operation code (opcode) and operands. An instruction can have one opcode and zero or more operands. Some common instruction formats are shown in Figure 6.1.

Figure 6.1 Opcode and operands

The operands are located either in registers (fast speed) or in a memory location. Table 6.1 lists some common classes of instructions.

Table 6.1 Common classes of instructions.

Memory to memory instructions Both operands are in memory

Memory to register instructions One of the operand is in memory, another one is in register

Register reference instructions The operation is performed on the contents of one or more registers

Memory reference instructions The operation is performed on the contents of memory location.

Control instructions Branching, halt, pause, and so on.

Input/output instructions Input or output

Macroinstructions A set of instructions

The logic instructions and arithmetic instructions are a subset of the memory and register reference instructions.

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