A MACRO is a abbrevation for a sequence of instrucions, logically sequenced to perform a operation.

When a corresponding language processor sees such a definition in the program, it assocites the sequence with the macro name and when it sees the abbrevated name it Replaces the whloe sequence whith entire sequence. this process is called Expension of Macros. this all happens at compile time but not at run time like subroutine calls.during the expansion MACRO definition disappears from the source code.

subrotine and macros:

"When ever a Macro name in the mnemonic field, assembly statment leads to its expansion it while when a subroutine name is seen it leads to its execution"

Using MACROs the 'instruction sequence' is repeated for every refference to Macro name while subroutine has only one copy of such a sequence which is reffred when ever a call is made when the program actualy runs. Macros are efficient in terms of speed as no extra processor cycles will be required to invoke the 'sequence' as the whole instruction sequence is inline.


Abhishek