Be careful when using Undocumented DOS Commands. Undocumented DOS Commands may not work with all versions of DOS. Most need DOS 4.0 or newer. Use them at your own risk.

In DOS 5.0 and newer, this can repair a master boot record and can sometimes rescue you in a bad situation by making an unbootable hard drive boot up. But...it might also trash your data and drive accessability,so you wouldn't want to use this unless you figure that things are so irreversably damaged or messed up that you have nothing to lose. It may make a bad situation worse if you have one or more of the following situations...

• You have a special driver for a large drive, such as disk manager or EZ-Drive.

• Your master boot record is infected with certain viruses.

• You have a multi-boot manager installed.

• Your bootable diskette and FDISK are from different versions of DOS. Best bet is to make a back-up of your drive (if possible) before trying to use the /MBR switch.

The U/ unconditionally formats your drive D:(or C:) without prompting you and without trying to leave behind the ability to later unformat the drive. The quickest possible format is
format /u/q.

This command works like the INSTALL command but it loads the program into upper memory. INSTALLHIGH also requires DOS 6.0 or newer and is for use in your Config.sys file.

Or you can use LH in DOS 5.0 and higher. The LH command isn't documented as shorthand for LOADHIGH but it should still work.

During the surface scan, the SCANDISK /TIME command marks as bad sectors that aren't readable but take longer than usual to read. This is a reasonable action to take because waiting until the sectors completely fail to read sectors can cause data loss. This command works in DOS 6.0 and higher.

In MS-DOS 5.0 and newer,adding the /R parameter causes the VER command to report(in addition to the DOS version)DOS' revision number and where DOS is loaded(in conventional memory,high memory or read-only memory).

The /-y tells the XCOPY command to not stop and prompt you for approval if it's about to over-write a file.

Don't use MS-DOS mode for a program if you see no benefit from doing so. There is a small risk involved with MS-DOS mode, because it gives a program total control of your hardware (including your hard drive!). If the program acts up and creates problems for your hard drives files, such as scrambling long file names, Win98 isn't there to prevent the problem (and results).