External And Internal DOS commands

UNDELETE Command

Use the UNDELETE command in later versions of DOS to try to recover deleted files. The

following are some variations of the UNDELETE command:

To undelete all files in the current directory:

UNDELETE *.*

To undelete the file TEST.TXT in the current directory:

UNDELETE TEST.TXT

To list the files that can be undeleted without actually undeleting them, use the following

command:

A:\UNDELETE /list

To recover deleted files without prompting for confirmation on each file, use the

following command:

A:\UNDELETE /all

When DOS deletes a file from a disk or hard drive, it does so as follows:

The first character of the filename in the root directory is overwritten with the character

s, which has the hex value E5.

All entries in the FAT for this file are replaced with 00s.

When you issue the DOS UNDELETE command, DOS looks for an entry in the root directory

matching the filename and replaces the first character of the filename in the root directory. From the root directory, DOS can read the starting cluster of the file and the size of the file. If the file is not too fragmented and the disk is otherwise healthy, DOS can locate the sectors belonging to the file and reconstruct the FAT.

RECOVER Command

The RECOVER command might mark clusters as bad in the FAT. Data that might have

been saved by other methods can sometimes be destroyed by the RECOVER command.

Don’t use this command without first making a DISKCOPY of the disk.

The RECOVER command attempts to recover a file from damaged sectors on a disk.

Always specify the drive, path, and filename of the file you want to recover with the

RECOVER command.

If you have several files that need recovering, use the command on one file at a time.

Sometimes the RECOVER command actually destroys data that might have been

recovered by some other method. As with CHKDSK, the file created by RECOVER

might need to be renamed so that its application recognizes it.

To recover the file named MYFILE.TXT, use the following command:

RECOVER MYFILE.TXT

Whatever portion of the file that the RECOVER command can read is stored in the root

directory and named A:FILE0000.REC (or a higher number). Copy this file to another disk

before trying to recover the next file.

There are applications like Norton Disk Doctor and PC Tools that do a better job than

RECOVER of recovering damaged files.

DISKCOPY Command

The DISKCOPY command makes an exact duplicate (sector by sector) of one disk (called

the source disk) to another disk of the same size and type (called the target disk).

To duplicate a disk using only a single drive, use the following command:

DISKCOPY A: A:

DOS prompts you as many times as necessary to insert the source disk and then insert the

target disk to make the exact copy.

Data is copied from one disk to the other byte by byte, including any hidden files, bad

sectors, fragmented files, or other contents. For this reason, the copy can be bad if the

source disk has some bad sectors.

DISKCOPY ignores sectors marked as bad in the FAT and copies to them anyway. The

DISKCOPY command copies formatting information, so the target disk does not need to

be formatted before executing the copy.