DOSBox is emulator software that emulates (loosely: "simulates") an IBM PC compatible computer running the older operating system, MS-DOS. Many IBM PC compatible graphics and sound cards are also emulated.
DOSBox provides a high level emulation of the DOS and BIOS interrupts, and contains its own internal DOS-like shell. This means that it can be used without owning a license to any real DOS operating system. Most commands that are typically used in installer batch files are supported, but many of the more advanced commands of later MS-DOS versions (e.g. post-Windows 98 DOS shells) are not. In addition to its internal shell, it also supports running image files of games and software originally intended to start without any operating system. The DOS emulation enables DOSBox to mount folders of the host OS as virtual drives.
It can also boot disk images with real DOS environments (MS-DOS, PC DOS, DR-DOS, FreeDOS, etc.) as well as other operating systems, including CP/M-86, Windows 3.1, and Windows 95.
DOSBox generally provides no hardware-level emulation. This means that the direct use of copy-protected physical media or of floppy disks in non-standard formats is generally not possible from DOSBox.