In Windows XP and before you can use the command "fixmbr" from the recovery console to do this. In Windows Vista and later, you need to execute "bootrec.exe /fixmbr".
winnt32/cmdcons
A Windows Boot Disk operates in DOS command line mode.
winreutil
Bcdedit.exe
Reinstall the IOS image. Recover a lost password
reinstall IOS imageformat flash file system
header record
LILO (LInux LOader)LILO stores information about the location of the kernel or other operating system on the Master Boot Record (MBR).GNU GRUB (GRand Unified Boot loader)GRUB has a more powerful, interactive command line interfaceRUB will default to its command line interface where the user can boot the system manually.GRUB may have difficulties booting certain hardware. LILO and GRUB do have a number of differences:* LILO has no interactive command interface, whereas GRUB does.* LILO does not support booting from a network, whereas GRUB does.* LILO stores information regarding the location of the operating systems it can to load physically on the MBR. If you change your LILO config file, you have to rewrite the LILO stage one boot loader to the MBR. Compared with GRUB, this is a much more risky option since a misconfigured MBR could leave the system unbootable. With GRUB, if the configuration file is configured incorrectly, it will simply default to the GRUB command-line interface. ---A2
Translation
In the Beginning... Was the Command Line was created in 1999.
In windows you can access DOS mode by clicking "run" in the start menu and typing "command" into the blank. DOS mode can also be accessed via the boot menu (accessed by pressing F8 during startup) and choosing command-line.
It is possible to boot MS-DOS or Linux from a USB Flash drive, but not all computers support doing it.