Difference between: Opcode, byte code, mnemonics, machine code and . . . Opcode: Opcode is short for operation code As its name suggests, the opcode is a type of code that tells the machine what to do, i e what operation to perform Opcode is a type of machine language instruction Bytecode: Bytecode is similar to opcode in nature, as it also tells the machine what to do
assembly - Intel x86 Opcode Reference? - Stack Overflow While Intel Software Developer's Manual itself is definitely not very convenient to search through, the opcode tables in this manual could help Take a look at the Appendix A "Opcode Map" in the volume 2A, 2B, 2C, and 2D of the manual, it might be useful:
assembly - How does an instruction decoder tell the difference between . . . The decoder has an undocumented (but easy to reverse) algorithm when picking up these prefixes This shows that some opcode listed in the manual is actually a prefix+opcode N B Is syntactically valid to add an unneeded prefix to an opcode, but it's a reserved use –
c - What is the actual relation between assembly, machine code . . . Opcode: The first one (or two) bytes of the machine code It acts like a selector to tell the CPU which microcode sequence the CPU it is to perform (something like a switch statement in C) Microcode: The hardwired instruction sequences within the CPU that are used to execute the machine code
How to read the Intel Opcode notation - Stack Overflow The opcode determines if the operand is a signed value All words, doublewords and quadwords are given with the low-order byte first • +rb, +rw, +rd, +ro — Indicates the lower 3 bits of the opcode byte is used to encode the register operand without a modR M byte The instruction lists the corresponding hexadecimal value of the opcode byte
What is the difference between Mnemonics and Opcode The opcode refers to the binary sequence that identifies the instruction So for the 8085 I believe 0x80 would be the opcode for "ADD B" A mnemonic is a human readable name that helps you remember the instructions So the string "ADD B" is a mnemonic for 0x80 "ADD B" is a lot easier to remember than 0x80
Why call instruction opcode is represented as FF15? Have a look at this question: what does opcode FF350E204000 do? It explains that an entire group of instructions starts with FF: INC , DEC , CALLN , CALLF , JMPN , JMPF , PUSH The instruction is determined by looking at bits 5 through 3 of the ModR M byte (see e g here if you want to avoid the official intel manual), that is in your case
What is the difference between machine code and opcode? The question is mostly related to PHP because IMHO opcode is mostly mentioned in PHP context In fact Java is more popular for its byte- opcode 1) Is opcode just a portion of machine code, does machine code consist of opcodes? Yes, but this opcodes are machine-dependent
Opcode vs Operand in x86 assembly source code - Stack Overflow where I said the mov was the opcode and [ax],0000h was the operand and together they formed an instruction My instructor gave me a 0 on the question and said that [ax] was the opcode and 0000h was the operand only In my textbook it says that in a MOV instruction the mov is the opcode and the source and destination are often called operands
assembly - Calculate the JMP opcodes - Stack Overflow The formula is fine (though it seems the provided assembly and addresses dont exactly match: 02980000 - 6259326b - 5 = c726cd90, reverse the byte order and it almost matches your correct assembly, Id assume its off due image relocation etc )