Definition: A directive is a statement in a program that provides guidance or instructions to the compiler or assembler. It is not executed at runtime but helps in the compilation or assembly process.
Purpose: Directives are used to control the assembly process, define constants, allocate storage, and manage sections of code.
Examples:
In assembly language, directives like .data and .text define data and code sections, respectively.
In C/C++, preprocessor directives such as #include, #define, and #ifdef are used to include files, define macros, and conditionally compile code.
Definition: An instruction is a command executed by the CPU. It is part of the machine code that performs operations on data, such as arithmetic, logic, control, and data movement.
Purpose: Instructions are used to perform tasks and operations on data during program execution. They are the fundamental operations that the CPU understands and executes.
Examples:
In assembly language, instructions like MOV, ADD, SUB, and JMP are used to move data, perform arithmetic, and control the flow of execution.
Execution: Directives are not executed at runtime; they guide the compilation or assembly process. Instructions are executed by the CPU during runtime.
Function: Directives manage how the program is translated into machine code, while instructions perform operations on data during program execution.
Context: Directives are often specific to the programming language or assembler being used, whereas instructions are specific to the CPU architecture.
Direct Memory Access (DMA)