先决条件 – 指令格式
1. 三地址说明：
三地址指令是机器指令的一种格式。它有一个操作码和三个地址字段。
2. 单一地址说明：
单地址指令也是一种格式。它只有两个字段。一个用于操作码，另一个用于操作数。
三地址指令和一地址指令的区别：
| Three-Address Instruction | One-Address Instruction |
|---|---|
| It has four fields. | It has only two fields. |
| It has one field for opcode and three fields for address. | It also has one field for opcode but there is only one field for address. |
| It has long instruction length. | It has shorter instruction. |
| There may be three memory accesses needed for an instruction. | There is a single memory access needed for an instruction. |
| It is slower accessing location inside processor than memory. | It is faster accessing location inside processor than memory. |
| It disadvantage i.e. three memory access is eliminated by two-address memory. | It eliminated two memory access. |
| There are three location for operand and result. | There is only one location for operand and result. |