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Q58123: "Feature Unavailable" Using FRE(-3) in .EXE Compiled in 7.00

Article: Q58123
Product(s): See article
Version(s): 7.00
Operating System(s): MS-DOS
Keyword(s): ENDUSER | SR# S900125-132 | mspl13_basic
Last Modified: 26-FEB-1990

The FRE(-3) function, which returns available expanded memory in the
QuickBASIC Extended (QBX.EXE) environment, normally gives a "Feature
Unavailable" (run-time error 73) in .EXE files created with BC.EXE. An
exception is if an executable .EXE file is linked with overlays that
are each no larger than 64K, and if a LIM 4.0 EMS expanded memory
driver (defined below) is installed, then the FRE(-3) function returns
a value for the amount of free expanded memory. This information
applies to Microsoft BASIC Professional Development System (PDS)
Version 7.00 for MS-DOS.

The FRE(-3) function returns the amount of free LIM 4.0 EMS expanded
memory available for arrays, SUBs, and functions in the QBX.EXE
environment.

Note that the only way that compiled BASIC .EXE applications can take
advantage of expanded memory is with linked overlays, but then only if
each overlay is smaller than 64K. (If expanded memory is not
accessible, overlays just swap to disk.) The FRE(-3) function returns
a value for an .EXE program only when a LIM 4.0 EMS driver is
installed and the .EXE program is able to successfully store its
overlays in expanded memory.

To check the amount of available expanded memory from an EXE program,
see Pages 204-206 in Ray Duncan's "Advanced MS-DOS Programming, 2nd
Edition" (Microsoft Press, 1988). The method described there uses
assembly language and interrupts.

Note: LIM 4.0 EMS is defined as follows:

   LIM  = Lotus, Intel, Microsoft
   4.0  = Version number 4.0 (of the standard LIM EMS)
   EMS  = Expanded Memory Specification, a standard for addressing
          expanded memory

For more information about linker overlays in BASIC PDS 7.00, search
for a separate article with the following keywords:

   BASIC and 7.00 and linker and overlays and modules

Also see Pages 612-614 of the "Microsoft BASIC 7.0: Programmer's
Guide," in the section "Linking with Overlays".

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