Slide 4.6: Filename extensions and comments

Slide 4.5: A sample program (ReadSub.asm)
Slide 4.7: INCLUDE directive
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Filename Extensions and Comments

Filename Extensions
A filename extension indicates the kind of data stored in the file.

Extension	Comments
`.ASM`	Assembly language source file (uncompiled)
`.BAT`	Batch file, ASCII file of DOS commands, [EXECUTABLE]
`.EXE`	Executable file (program) (binary) [EXECUTABLE]
`.LST`	List file
`.MAP`	A text file that contains information about the segments contained in a program being linked
`.OBJ`	Object file
`.PDB`	The program database file with which the debugger is then able to display the program's source code and provide supplemental information about the program.

TITLE Directive
A directive is a command that is recognized and acted upon by the assembler. It is not related to the Intel instruction set. Directives are used for defining logical segments, choosing a memory model, defining variables, creating procedures, and so on.

   TITLE  Read and Subtract     (ReadSub.asm)

The TITLE directive marks the entire line as a comment.

Comments
Comments can be specified in two ways:

Single-line comments, beginning with a semicolon character (;).
```
call   WriteString              ; print prompt1
```
Block comments, beginning with the COMMENT directive and a user specified symbol such as (!).
```
COMMENT  !
  This program reads and subtracts 32-bit integers.
!
```