Prerequisite – Instruction Formats
1. Three-Address Instructions:
Three-address instruction is a format of machine instruction. It has one opcode and three address fields.
2. One-Address Instructions:
One-Address instruction is also a format. It has only two fields. One for opcode and other for operand.
Difference between Three-Address Instruction and One-Address Instruction:
| 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. |
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