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2.4 Instruction Format

The information encoded in an 80386 instruction includes a specification of the operation to be performed, the type of the operands to be manipulated, and the location of these operands. If an operand is located in memory, the instruction must also select, explicitly or implicitly, which of the currently addressable segments contains the operand.

80386 instructions are composed of various elements and have various formats. The exact format of instructions is shown in Appendix B; the elements of instructions are described below. Of these instruction elements, only one, the opcode, is always present. The other elements may or may not be present, depending on the particular operation involved and on the location and type of the operands. The elements of an instruction, in order of occurrence are as follows:


up: Chapter 2 -- Basic Programming Model
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