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Q64876: "Insufficient EMS to Load Overlays" at Run Time in 7.00, 7.10

Article: Q64876
Product(s): See article
Version(s): 7.00 7.10
Operating System(s): MS-DOS
Keyword(s): ENDUSER | SR# S900808-19 | mspl13_basic
Last Modified: 5-SEP-1990

The run-time error message "Insufficient EMS to load overlays" occurs
(if it is going to occur at all) when the first overlaid module is
called. This error is documented on Page 656 of the "Microsoft BASIC
7.0: Language Reference" manual for Microsoft BASIC Professional
Development System (PDS) versions 7.00 and 7.10. The article below
explains in more detail why you might get this error condition.

This information applies to Microsoft BASIC Professional Development
System (PDS) versions 7.00 and 7.10 for MS-DOS when using linked
overlays.

The "Insufficient EMS to load overlays" error message is not random.
If you run a program on a particular machine and the error does not
occur, the error will never occur for that program unless that
machine's expanded memory configuration is changed. Common ways of
changing the expanded memory configuration include the following:
setting up a larger RAM drive in expanded memory; or moving the
program to another machine with a different amount of free expanded
memory.

If a given program produces an "Insufficient EMS to load overlays"
error on a given machine, the error will always occur for that program
as long as the machine's expanded memory configuration and usage stay
the same.

When a BASIC program calls the first overlaid module, the program
must estimate the space in expanded memory necessary to load all
overlays at once. This estimate is based only on the following:

1. The number of overlays
2. The size of the largest overlay
3. The fact that each overlay has less than 64K of code (otherwise, it
   would not be able to use expanded memory)

The overlay manager in BASIC 7.00 and 7.10 requests expanded memory in
16K pages (blocks). The overlay manager knows the size of only the
largest overlay and must make a "best guess" at the size of the
smaller overlays. When the overlay manager estimates how many 16K
pages are necessary to hold all overlays at once in expanded memory,
the estimate could be over or under the actual number of pages needed.
If your overlays are all between 16K and 64K in size (according to the
LINK .MAP file), and if the estimated or actual size of all overlays
together exceeds the available expanded memory, the following
initialization error occurs when the first overlay is called at
run-time:

   Insufficient EMS to load overlays

Note: You will never see this error if all your overlays are smaller
than 16K each.

If you want to force loading overlays from disk, thus avoiding the
possibility of this overlay-initialization error in expanded memory,
you must link with the stub file NOEMS.OBJ (with no parentheses around
NOEMS.OBJ on the LINK command line). Alternatively, you can try
reconfiguring expanded memory so more of it is available for BASIC
overlays. Another alternative is to make overlays similar in size.

To find out the size of each overlay, you must look at the .MAP file
generated by the linker (LINK.EXE).

References:

For more information about how to use link overlays in BASIC 7.00 and
7.10, search in this Knowledge Base for a separate article with the
following words:

   How and link and overlays and expanded and memory and BASIC

See also the section "Linking with Overlays" on Pages 612-614 in the
"Microsoft BASIC 7.0: Programmer's Guide" for versions 7.00 and 7.10.

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