Common Terminologies

1. Mnemonic: The actual CPU operation.
2. Operand: Arguments passed to the mnemonic, which could be a register, intermediate or a memory location.
3. Instruction: Something the CPU can execute. It includes both the mnemonic and the operands.
4. Immediate: An immediate is a constant value, like 4.
5. Label: A name given to a particular memory address in the code.
   • It is made up of letters, digits and underscore.
   • A label must start with a letter or underscore.
   • A label must end with a colon.
   • There are . prepended labels which are used to make a label available to its parent and hides from others. Just don’t think about it for now, it’s a complicated thing.
   • It holds meaning for the assembler (GAS, in our case), not the CPU. The assembler replaces the labels with virtual addresses or offsets.
6. Directive (or Pseudo-Instruction): Instructions defined for the assembler program, not the CPU.
   • They begin with a period (.).
   • Ex: .section creates a section within the program.
7. Section: The code is divided into multiple sections to organize the memory layout.
8. Comment: Anything after a semi-colon (;) or hash (#) is ignored by the assembler and is a note for the programmer itself.
9. Keyword: In high-level languages, keywords are reserved words (like if, for, while). In assembly, the idea of keywords basically overlaps with mnemonics and directives.
10. Symbol: Everything is a symbol. More on this in future.