unDOS

unDOS emulates the most commonly used DOS and BIOS functions, most notably the int 21h and int 1h services. This allows new or existing applications for Intel 80x86 embedded systems to get away from DOS for reasons such as avoiding DOS royalties, freeing up the memory used by DOS, and porting an existing application to protected mode without needing a DOS extender.
Unlike smx and other Micro Digital products, unDOS is sold on a no-royalty basis. Since only the most used DOS functions are emulated, it takes less memory than DOS, thus giving real mode applications more space in precious real memory.
unDOS replacements for DOS and BIOS services are linked with your application code, so if your applications runs in protected mode, so too do the unDOS services. DOS extenders, by contrast, switch to real mode or virtual 86 mode to perform DOS or BIOS functions, using DOS to do the work and then returning the result to the protected mode application. This switching to real/virtual 86 mode is undesirable for embedded systems because it greatly increases interrupt latency, delays task switching because DOS extenders cannot be preempted, and complicates debugging. Thus, unDOS is a simpler alternative to a DOS extender.
unDOS is a bridge product which helps embedded system developers migrate their applications to protected mode, where DOS functions are no longer accessible, or allows real mode programs to run without DOS.