◄Up► ◄Contents► ◄Index► ◄Back►
─────Using Overlays─────────────────────────────────────────────────────────
 
     LINK can create DOS programs with overlays. Overlays are parts of
     a program that are loaded into memory only when needed. Overlays
     share the same space in memory.
 
     Specifying Overlays
 
     Specify overlays by grouping object files in parentheses.
     See: ◄Overlay Syntax►
 
     How Overlays Work
 
     The overlay-manager code is included as part of the language's
     default libraries. If you specify overlays during linking, the
     code for the overlay manager is automatically linked with the rest
     of your program. LINK produces only one .EXE file. This file is
     read again and again as long as the overlay manager needs to
     extract overlaid object files. When a program cannot find a needed
     file containing an overlay, it generates prompts.
     See: ◄Overlay-Manager Prompts►
 
     Only code is overlaid, not data. Programs that use overlays
     usually require less memory. However, they run more slowly because
     of the time needed to load and reload the code from disk into
     memory. Not all programs can use overlays.
     See: ◄Restrictions on Overlays►
 
     Overlay Interrupts
 
     LINK replaces far calls to routines in overlays with interrupts
     (followed by the module identifier and offset). By default, the
     interrupt number is 63 (3F hexadecimal). Use the /OV option to
     change the interrupt number.
     See: ◄/OV Option►
 
     WARNING: Never rename an executable program file containing
              overlays if it is to run under DOS 2.x and earlier. LINK
              records the .EXE filename in the program file. If you
              rename the file, the overlay manager may not be able to
              locate the proper file. You can rename an .EXE file that
              will run under DOS 3.x and later.
                                    -♦-