ARCHIVED: In DOS, what does the CHKDSK (check disk) command do?
Usage
The CHKDSK
(CHecK DiSK) command reports on a number of
items concerning your drive, the amount of space used, and the amount
of space still available. The first five to six lines report
information about your hard disk.
The syntax for CHKDSK
is:
CHKDSK [drive:][[path]filename] [/F] [/V]
The drive:
and path
parameters specify
the drive and directory to check, and filename
specifies
the file(s) to check. The following switches are also available:
- Use
/F
to fix errors reported on the disk, such as "Lost Allocation Units". - Use
/V
to show the full path and name of each file on that disk.
To check the current disk, use CHKDSK
with no
parameters:
CHKDSK
Bad sectors
Do not be alarmed by sectors on your disk that are labeled "bad sector". When hard disks are manufactured, there are sometimes minute flaws in the surface of the disk that would not be good for storing data. When a hard disk is formatted, DOS inspects the disk, marks any questionable areas as bad sectors, and prohibits data from being written to these areas. There is no current problem with the disk, and you don't need to do anything.
Error messages about lost chains
When DOS saves a file, it places an End of File marker at the very
end of the file. In addition, the information about the location and
length of the file is kept in the File Allocation Table (FAT). This is
what you see when you enter DIR
at the command
prompt.
If, for some reason, a computer fails to save all of a file (if the power goes out, the computer gets turned off, or the computer gets rebooted), DOS cannot mark the end of the file, and the FAT table is incomplete. DOS knows where the file starts, but is unsure of where it ends. The last few unidentified, unattached bits of file are called "lost chains". You should see:
Convert Lost Chains to Files (Y/N)?
After looking at the CHKDSK
report, start the process
over again, but enter CHKDSK/F
. When you enter
just CHKDSK
, you cannot have it fix the problems whether
you press y
or n
.
The /F
is a parameter that tells DOS that you want to
fix the problems.
DOS will let you take the information in these lost chains and save
it to a file, so you can review it to see if it contains information
that you need to salvage. Answer the question above by pressing either
y
to make these files or
n
to erase the chains and not make files.
If you press y
to save files, they are put
in the root directory of the current logged drive. DOS saves the
information in files named FILE0000.CHK
,
FILE0001.CHK
, and so on, creating one file for each lost
chain. To look at them, enter:
TYPE FILE0000.CHK | More
The vertical line is a DOS pipe command, allowing you to place two
commands on the same line. The More
command prints a
single screen of information at a time. If the information in these
files is garbage (unintelligible characters and beeps), delete the
file by entering:
DEL FILE000.CHK
Allocation units
The allocation units in the above example are reported on computers that have DOS 4.0 or later. It is an indication of the smallest storage unit on the drive. In this case, that is 2048 bytes. In other words, when you create a batch file that has 52 bytes, you will have to use 2048 bytes disk space to save it.
Related tools
Microsoft ScanDisk is a disk analysis and repair tool packaged with MS-DOS 6.2 that checks a drive for errors and corrects any problems it finds.
To check the current drive for disk errors, use:
SCANDISK
This is document aall in the Knowledge Base.
Last modified on 2018-01-18 08:52:01.