Here's a DOS trick for Windows 9x, that will reset (delete) your motherboard's
BIOS password (aka CMOS password) without any need to open up your computer
to remove the battery or mess with jumpers.
This method can come in very handy in the event you ever lose and forget your
BIOS password or if you acquire used computers where the unknown previous owners
had BIOS passwords set (in fact, this happened to me long agoI was given
a used computer, but there was no way I could enter the CMOS to make changes).
It's important to note here that the password we are talking about is only the
one that prevents a user from entering the BIOS setup at bootup, not the one
that stops you from getting past the boot.
Normally, at bootup you can press a key (usually the DEL key) to access your
BIOS allowing you to view it or make changes. With a password set, there is
no way to enter setup. Though a password can provide a basic and very effective
level of PC security, losing it can be a real headache if you don't know how
to fix the problem.
The MS-DOS command that will makes this trick possible is the DEBUG command
(debug itself is a utilitydebug.exewhich is located in your Windows
Command folder). This is not a command to be taken lightlyin other
words, it's not a command to play with! You can cause serious corruption with
this command and can end up not being able to even boot your computer! Debug
is used to work with binary and executable files and allows you to alter (hex
edit) the contents of a file or CPU register right down to the binary and byte
To begin debug mode, type debug at a MS-DOS prompt or you can specify
a file, i.e., DEBUG FILE.EXE. There is a difference in screen output
between the two methods. When you type DEBUG alone, debug responds with
a hyphen (-) prompt waiting for you to enter commands. The second method, with
a file specified, loads the file into memory and you type all the commands on
the line used to start debug. In this tip, we will be writing to the BIOS, so
the first method is the one that would be used. All debug commands can be aborted
at any time by pressing CTRL/C.
Accessing BIOS with DEBUG
The basic trick will be to fool the BIOS into thinking there is a checksum
error, in which case it resets itself, including the password. This is done
by invalidating the CMOS and to do that we must know how to access the BIOS
and where the checksum value of the CMOS is located so that we can change it.
Access to the the BIOS content is via what are known as CMOS Ports and
it's Port 70 and 71 that will give us the needed access. On almost
all AT motherboards, the checksum is located at hexadecimal address 2e and
2f and filling the address 2e with ff is all you should
have to do to invalidate the checksum.
Here's what to do if you ever need to reset the password and have no other
method, and you don't want to open up your computer to remove the battery or
Note! Do this at your own risk. I can only tell you that it has worked for
me more than once and has worked for others as well. But I cannot make any guarantees.
When I did this, I took a willing risk. The BIOS was Award Modular BIOS
- Restart your computer in MS-DOS mode.
- When you get to the C:\> or C:\WINDOWS> prompt, type
DEBUG and press Enter.
- A hyphen (-) prompt will appear waiting for you to enter commands.
- Enter the following commands, pressing Enter after each one.
Note: the o is the letter o and stands for OUTPUT.
- After the q command (which stands for QUIT), enter Exit.
- Then try to enter your BIOS at bootup. The password prompt should now be
gone and you should now have full access to it again. However, you will now
be at the default BIOS setttings and may want to change them to your preference.
You may also want to have your drives autodetected again.
In closing, I should state that in the case of a lost BIOS password, your first
step should always be to contact your manufacturer to see if a backdoor password
is available that will allow you to bypass the forgotten password.
There are many sites on the net that list backdoor passwords you can try, but
beware that some BIOS that are set up to lock up if you enter the wrong password
more than a certain number of times, usually only 3 times!
For more Windows tips and tricks, join Vic's popular user group at: http://groups.yahoo.com/group/WinTips-Tricks/
For another debug use and example, see my article on creating your own color
And speaking of color, if you happen to be gettting into the world of DVDs
and are confused by it all, check out my new Experts Guides on video, audio,
Playstation, and computers: http://www.angelfire.com/va3/expert_guides