MSDOS.SYS

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MSDOS.SYS

One of two hidden system files that made up Microsoft's MS-DOS. The other was IO.SYS. These two system files were loaded into memory when the computer was booted. They processed the instructions in CONFIG.SYS, then loaded COMMAND.COM and finally processed the instructions in AUTOEXEC.BAT. The PC-DOS counterparts of these system files were IBMBIO.COM and IBMDOS.COM.

From Executable to Text
In Windows 95/98, MSDOS.SYS was changed to a text configuration file rather than an executable program. It determined among other things whether the computer booted into DOS or Windows. IO.SYS was still a binary executable.
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References in periodicals archive ?
This drive must have the following three programs or their equivalents: IO.
This destroys the master boot record, the root directory, the file-allocation tables and programs such as IO.