Assembly Language Concepts: A Comprehensive Guide
| System Software | Application Software |
|---|---|
| Manages and controls computer hardware and resources | Performs specific tasks for end users |
Interfaces between hardware and application software | Interfaces between system software and end users |
Operating systems, device drivers, utility programs | Web browsers, word processors, spreadsheet software |
| General-purpose software | Specific-purpose software |
| Typically written in low-level languages | Usually written in high-level languages |
| Literal | Immediate Operand |
|---|---|
| A constant value specified in the assembly language program that is not part of the machine instruction | A constant value that is encoded directly into the machine instruction |
The assembler generates the literal value as a constant at a separate memory location. The address of this constant is used as the operand in the machine instruction | The immediate value is assembled as part of the machine instruction itself |
The literal is specified using special syntax like ‘=value‘ | The immediate value is encoded directly in the instruction operand field |
Used when the constant does not fit in the immediate field of the instruction or when the constant needs to be stored in memory | Used when the constant fits in the immediate field and doesn’t need to be stored in memory |
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|
| Macro | Function |
|---|---|
| Macro is preprocessed. | Function is compiled. |
| Macro does not support type checking. | Function supports type checking. |
| Program length increases. | Program length remains the same. |
| There is a side effect when using a macro. | No side effect when using a function. |
| Execution is faster. | Execution is slower. |
Useful where small source code appears many times. | Useful where large source code appears many times. |
| Macro does not check compile errors. | Function checks compile errors. |
Before compilation, the macro name is replaced by the macro value. | During the function call, the transfer of control takes place. |
| Macro | Procedure |
|---|---|
| The corresponding machine code is written every time a macro is called in a program. | The corresponding machine code is written only once in memory. |
| Requires more memory space for the program. | Requires less memory space for the program. |
| No transfer of program counter. | Transferring of the program counter is required. |
| Faster execution. | Slower execution. |
| Assembly time is more. | Assembly time is less. |
No overhead of using the stack for transferring control. | Overhead of using the stack for transferring control. |
| Interpreter | Compiler |
|---|---|
The source program is interpreted every time it is to be executed, and every time the source program is analyzed. Hence, interpretation is less efficient than compilation. | In the process of compilation, the program is analyzed only once, and then the code is generated. Hence, the compiler is more efficient than the interpreter. |
| Interpreters do not produce object code. | Compilers produce object code. |
| Interpreters can be made portable because they do not produce object code. | The compiler has to be present on the host machine when a particular program needs to be compiled. |
| Interpreters are simpler and give us an improved debugging environment. | The compiler is a complex program and requires a large amount of memory. |
| One Pass | Two Pass |
|---|---|
| It performs translation in one pass. | It performs translation in two passes. |
| It scans the entire file only once. | It requires two passes to scan the source file. |
| It generates intermediate code. | It does not generate intermediate code. |
Data structure: Symbol table, literal table, pool table, and table of incomplete instructions. | Data structure: Symbol table, literal table, and pool table. |
| Perform some processing of assembler directives. | Perform processing of assembler directives not done in Pass – 1. |
| It is faster than a two-pass assembler. | It is slower than a one-pass assembler. |
| No object program is written; hence, no loader is required. | The loader is required as the object code is generated. |
Macro Call
- This is the point in the source code where the macro name is used. It’s like invoking a function.
- The compiler encounters the macro name and recognizes it as a macro.
- The compiler then replaces the macro call with the corresponding macro body.
Macro Expansion
- This is the process of replacing the macro call with its macro body.
- The compiler substitutes the actual arguments provided in the macro call for the formal parameters defined in the macro.
- The resulting expanded code is then inserted into the source code where the macro call was originally located.
