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DOS/4G is a 32-bit DOS extender developed by Rational Systems (now Tenberry Software). It allows DOS programs to eliminate the 640 KB conventional memory limit by addressing up to 64 MB of extended memory on Intel 80386 and above machines.
2.01 / April 3, 1996
Functioning as a highly flexible and reusable memory extension library, DOS/4G allowed programmers to access extended memory without programming specialized code. It embeds itself in the executable file at linking time and executes before main application code, so usually DOS/4G initialization messages show up at launch. It can operate within MS-DOS, PC DOS, DR-DOS and other DOS clones, the DOS boxes of OS/2, Microsoft Windows, Windows NT and Windows 95, and DOS emulators such as DOSBox.
Initial versions of DOS/4G had trouble with secondary DMA channels on the ISA bus, which prevented 16-bit devices like Gravis Ultrasound series from normally functioning; Gravis even had to develop PREPGAME, a patch utility which updated the game executable with a new version 1.97 to fix the incompatibility.