General discussion

System CMOS check sum bad

I keep getting error messages when I start my computer. error 0271 check date&time. error 0251 System CMOS check sum bad. I tried two system restores but it failed. can anyone help me? I have an emachine model T 2542 year 2002 windows xp.

Discussion is locked
Reply to: System CMOS check sum bad
PLEASE NOTE: Do not post advertisements, offensive materials, profanity, or personal attacks. Please remember to be considerate of other members. If you are new to the CNET Forums, please read our CNET Forums FAQ. All submitted content is subject to our Terms of Use.
Reporting: System CMOS check sum bad
This post has been flagged and will be reviewed by our staff. Thank you for helping us maintain CNET's great community.
Sorry, there was a problem flagging this post. Please try again now or at a later time.
If you believe this post is offensive or violates the CNET Forums' Usage policies, you can report it below (this will not automatically remove the post). Once reported, our moderators will be notified and the post will be reviewed.
- Collapse -
Re: system CMOS checksum bad.

That's not something you can change in System Restore. It's in the BIOS, and it's shown long before the machine even knows there's something like Windows going to run ten seconds later.

The usual remedies are:
- At boot, go into the BIOS setup screen (that's something like pressing del or escape or F2 or another key or key combination, depending on the motherboard, mostly it's shown on the screen) and find out how to reset it back to defaults. While there, check the date and time also.
- Replace the battery on the motherboard.

But it's possible it points to a more serious hardware error.

Hope this helps.


- Collapse -
Just the battery.

Kees is right. If you reconfigure your bios and change the system time and date that error will not come back until you lose power to the computer. As long as it stays plugged in, it shouldn't happen.

- Collapse -
re: CMOS check sum bad

The "CMOS check sum bad" message usually means that the self check of itself (the BIOS checking on the contents of itself) does not check properly.

It does this at initial system start, there is a routine that does a summation and sort of verification of all of the code there - not the settings, which can be variable, just the code. The code does not change from bootup to bootup. It remains constant.

If ever you update your BIOS the routine has a new checksum number value that is only valid for that new code.

When the checksum evaluation does not match the contained value that error message will happen.
Your trouble, I suspect, is something has buggered up at least one bit (perhaps more, and even if it is one bit, who's to say how it is going to affect your computer) that could totally screw with your computer's operation.

Get the latest BIOS update from your computer manufacturer's website and try to re-flash it.

Once that is done, re-set all of your needed settings, and if it can't hold the date and time for any period of power off time, then replace the battery.

- Collapse -
Why date error is reported before checksum error

If the data and time error message is reported before the checksum error that would be from a quick check of a timing loop, just to see if the clock seems to be running. The BIOS has almost no idea if any one date is any more correct than any other date. So, just being off a few minutes, hours, even days, maybe more, is NOT going to trigger a "date & time" error message.

Instead, the BIOS has a quick routine just to see of the clock seems to be running at a reasonable rate (there is a lot of latitude). Running 5 or 10% faster or slower may not trigger such an error message, but if the clock pulses are off more substantial intervals then that error message should result. After all, if the clock pulse (not the actual time, but the "beats of the clock") is off, how can you trust anything else? The next thing the BIOS is going to do is to do a checksum of the actual contents of the BIOS code.

Now, you've already seen that the checksum error was being reported. Not you, or anyone, can tell if the part of the invalid code is in the timing loop to check the clock pulses, or anywhere else. Besides, it doesn't matter. If the code is bad (the checksum error) then you really can't trust anything to work properly. It may just be coincidence if your computer boots up at all.

- Collapse -
You all fail.

Check sum is a settings (yeah variable) measure. It is making sure that your settings have not changed by logging the sum of the values of your settings. If your cmos accidentally read your proc clock multiplier as 111 instead of 11, your computer would die.

So if any settings are corrupt, defaults are loaded. Corrupt settings means the battery is dead/dying.

The time error occurs when the date on the system is before the date of the BIOS release.

CNET Forums