Each time you turn on your computer, it will check on the control file
-
Command.com, io.sys
-
Command.com, date.com, dir.com
-
Command.com, io.sys, msdos.sys
-
Chkdsk.exe
During boot process, DOS checks critical system files that initialize the operating system. COMMAND.COM provides the command interpreter, IO.SYS handles basic input/output operations, and MSDOS.SYS contains the MS-DOS kernel. These three files work together to start the system properly. Other options include incorrect file combinations or utilities not required for booting.
On boot, MS-DOS/early Windows systems check for the core system files COMMAND.COM (the command interpreter), IO.SYS, and MSDOS.SYS (the two hidden kernel/BIOS-interface files) — these three must be present and in the right order for the machine to boot into DOS. Command.com plus date.com/dir.com or chkdsk.exe are just ordinary utility programs, not boot-critical system files, so those options are incorrect.