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 Dual mode
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 The ability to create dual mode programs simply by adding a single command
 to the link script file is a major breakthrough. Dual mode programs detect
 at startup whether there are enough system resources to run in protected
 mode. If there are insufficient resources then the same program will run
 within the 640 Kb real mode memory limit as a dynamically overlaid program.
 The .EXE still only consists of one program capable of operating in either
 mode, it is not two separate copies joined together in some way. There is
 negligible increase in .EXE size over a single mode program, and a similarly
 negligible overhead in execution speed, since the whole program is loaded
 into memory when running in protected mode.

 For this dual mode to work and be effective, all code must be written to
 execute in both real and protected mode. High level languages, such as
 CA-Clipper, require no code changes whatsoever to run in protected mode, and
 changes for C, PASCAL and FORTRAN are the exception rather than the rule.
 This requirement should only affect high level C and ASM programmers. In the
 worst case the code should be able to test for the processor mode each time
 it is executed and then jump to the appropriate code.

 We suggest that C and ASM programmers do not create a protected mode library
 separate from the real mode library, since both types of code will have to
 be linked in at link time to create a dual mode program. The benefits of
 writing dual mode code and creating a dual mode library include :

 . Only one copy of the source code and one library to maintain.
 . Less disk space requirement for distribution.
 . Less technical support with people linking the wrong library.