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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[2] MB of extended memory on Intel 80386 and above machines.

Developer(s) Tenberry Software
Stable release
2.01 / April 3, 1996; 21 years ago (1996-04-03)[1]
Development status Abandonware
Operating system DOS
Platform IA-32
Type DOS extender
License Proprietary



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.


DOS/4GW 1.95 was a free limited edition of DOS/4G and was included with the Watcom C compiler with a commercial re-distribution license. It was made widely popular by computer games like Doom.

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.

In case of problems, DOS/4G or DOS/4GW can be replaced with the newer and free DOS/32; a patch utility can even replace DOS/4G code embedded inside a compiled executable file.[3]

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