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IBM/Intel/Windows PC BIOS Tick-Over Bug


In spite of what you may have heard, PC hardware is mostly OK when it comes to the Year 2000. However, many older machines have a minor hardware problem with their BIOS (want to know what that is? see's PC Webopaedia's BIOS entry) that prevents the year part of the system date from automatically changing from 1999 to 2000. This problem is commonly known as the “Tick-Over Problem”; it's usually easy to fix, often without cost.

The tick-over problem is most common on 486 and older PCs, however, as of July, 1998, some newly manufactured Pentium II PCs are still being sold that contain this problem. We have confirmed that the numerous Dell 486 and early Pentium machines on campus do have the tick-over bug.

Most machines with the tick-over bug don't actually have problems with dates in the 2000s; they just can't automatically change the year from the year 1999 to the year 2000. So often the fix is just to reboot the machine sometime on or after January 1, 2000, and to manually change the date just once. Some are fixed a bit differently -- you download and run a free software BIOS upgrade. That you can at any time; you don't need to wait until 2000.

Finding and Fixing the Tick-Over Bug
  Step 1: Test your computer using the safe procedure given below. (It's not a bad idea to carefully test your machine even if its manufacturer says it doesn't have the problem.)

If your computer passes the tests, you do not need to do anything for the century change. (Don't forget to set the date back to the current date when you are done testing!)

Step 2. If you found that you have the tick-over problem, check with the manufacturer's Web page to see whether you have a Flash BIOS that can be updated with software.

Step 3a. If you have the tick-over problem and the manufacturer says that you need a BIOS upgrade (either Flash or by purchasing a new BIOS), follow their instructions. (You could probably also get by with the simpler fix described below, but upgrading a flash BIOS is relatively painless and there are advantages to having the newest possible BIOS version, or at least so says Dell. A newer BIOS can result in fewer problems when you install new hardware.)

Note: Dell and many other PC manufacturers also provide a software upgrade for older machines without flash BIOS. You don't really need do to use that -- the procedure outlined Step 3b is easier to use and should work just fine for these machine. (And the testing described in that section will allow you to see whether it will work for your machine.)

Dell says that their OptiPlex XL/XM/XMT 5xx machines, which includes the Dell Pentiums purchased in the UIC Network Initiative (or perhaps you know it as ITIP --  Instructional Technology Improvement Program), fall in this category -- they have the tick-over problem and there's a flash BIOS upgrade for them. Their flash BIOS fix is in the Dell File Library at

The steps you follow to flash BIOS (according to Dell) are:

Step 3a-1. Save file to the hard drive

Step 3b-2. Restart Windows in MS-DOS mode

Step 3b-3. Go to the location on the drive where the file is stored

Step 3b-4. Type in the filename (without file extension)

Step 3b-5. Press Enter and follow the instructions

It's a good idea to run through the testing process again after you apply the BIOS fix.

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Step 3b. If you have the tick-over problem and you don't have flash BIOS. If you found you have the tick-over problem and it's the most common type -- the one that can be fixed just by resetting the date on your computer once; the testing procedure will tell you whether this is enough to fix your problem -- continue with the following steps.

Step 3b-1. Turn off your on the evening of December 31, 1999 and go to a party to toast in the New Year. If your computer functions as a server, you might need to leave it on. In that case, you should leave a bootable disk in the floppy drive, so that if there is a power interruption it will not come back up and run production software on the wrong date.

Step 3b-2. After the New Year, boot your computer from a boot floppy disk. (If you left your PC on over the night of December 31, 1999 to January 1, 1999, power it down and back up again.) It will probably show the date as 01-04-1980.

Step 3b-3. Manually set the date and time to the correct date and time as described below, specifying all four digits of the year (e.g. 1-1-2000). Don't forget to also set the time, as it will have been reset too.

Step 3b-4. Take the boot disk out and reboot normally. You have now successfully circumvented the Tick-Over Problem, until the year 2099 when it will happen again.

Step 3c. If you have the tick-over problem and the procedure outlined in Step 3b doesn't fix it.
If you found you have the tick-over problem it wasn't fixed by resetting the date on or after 1-1-2000 with all four digits for the year, you should ???.

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Safely Testing your PC's BIOS for the Year 2000 Tick-Over Problem
  Disclaimer: This testing procedure has been found to be safe for installed software and data on the computers which we have tried it on, and it has been found to be an accurate test for the presence or absence of the described problem. If you do not follow these instructions exactly, in particular as to when you must leave the Boot Disk in your floppy drive, or as to the requirement to set the clock back at the end of testing, this procedure could pose a hazard.

Follow these instructions exactly!

A note about date formats in this section: Although ISO 8601: Right Format for Dates insists that the format yyyy-mm-dd should be used everywhere, the default date format on PC systems is mm-dd-yy or mm-dd-yyyy, so that is how it is represented here.

To test for the tick-over problem, you will have to change the date and time settings of your computer's hardware clock. Casually fiddling with these settings is well known to be dangerous. Data can be lost. The Registry can become corrupted. Databases can become polluted with invalid data. The literature is filled with horror stories. Many, many people will simply tell you not to do it.

However, we are going to do it anyway. In order to do it safely, we will do all of our testing from a bootable floppy disk. Once this bootable floppy disk is created, leave it in the floppy drive, so that it boots from the floppy disk each time you reboot during the testing. Its presence in the floppy drive will safeguard the programs and data on your regular hard drive, and the PC will not be able to connect to the network since it will lack the necessary network drivers. Again: Don't removed the boot floppy from its drive until after testing is complete and the date and time are reset to the present.

During testing, do not attempt to access any programs or data files on your hard drive(s). In particular, do not change the current drive to the C: drive at any time during this test procedure.

Don't forget the final step of the test, which is to reset your computer's date and time back to the present!

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Procedure for Testing Your Computer:
  1. Create a Bootable DOS Floppy Disk in Windows or DOS.

(OS/2 users: Follow the OS/2 "Create Utility Diskettes" procedure. Linux users: see the Linux Bootdisk HOWTO at for instructions. However Linux and OS/2 users will probably find it much easier to borrow a DOS Boot Disk from another computer that has DOS or Windows installed.)

  1. Insert a blank floppy.
  2. If in Windows (any version), open a MS/DOS window.
  3. Format the floppy with system files by entering the command: format a: /s /u
2. Shut down your system normally, then press Ctrl-Alt-Delete to boot from the floppy disk.

3. If your computer won't boot from the floppy disk, but instead booted from the hard drive and brought up your regular system, you will need to go into your computer's System Setup Program and enable the option for booting from the floppy drive. On many of the Dell PCs here at UIC, that is done by:

  1. Reboot the computer
  2. When the computer beeps, immediately press Ctrl-Alt-Delete.
  3. You should now see the System Setup screen. If the option "Boot Sequence:" is not shown on this screen, press Alt-p to page through the screens until you find it.
  4. Change the value of "Boot Sequence:" to "Diskette First".
  5. Press Alt-b to save this setting and reboot again.
Other models of PCs may have a different procedure for this; consult your PC's manual.

If you have to change your System Setup Program setting, remember to set it back to the original setting when you finish testing.

3. When it boots from the floppy, reset the date to 12-31-1999 and the time to 23:59. Your computer may show you the date and time and ask you to set a new date and time; if it doesn't (DOS boot disks made on systems such as Windows 95 won't), use the date and time commands as shown below. (You enter the items shown in bold.)

Starting Windows 95...
Microsoft(R) Windows 95
   (C)Copyright Microsoft Corp 1981-1995.
Current date is Mon 07-06-1998
Enter new date (mm-dd-yy): 12-31-1999
Current time is 12:12:34.21p
Enter new time: 23:59
5. Turn off your computer's power and wait at least one minute.

It is necessary to have power completely turned off for this test to detect a malfunctioning BIOS. Ctrl-Alt-Delete or pressing the "Reset" button won't work; you must turn the power switch off to force the BIOS to read the CMOS  (want to know what that is? see's PC Webopaedia's CMOS entry) hardware clock again. It must be in a powered-off state at the moment of midnight on January 1, 2000, since that is when the problem occurs.

6. Double check that the floppy boot diskette is still in its drive, then turn your computer on, and let it boot from the floppy.

7. What is its date setting? (If it is one of the systems such as Windows 95 that does not ask you for a date setting when it boots, enter the date command to find out.)

8. The date should be Sat 01-01-2000. If it says the date is any other date (01-04-1980 is common) you have the tick-over bug.

9. Set the time and date again to 12-31-1999 23:59, but this time leave your computer on. Wait one minute and then verify that the date is Sat 01-01-2000. (The tick-over problem occurs when the year changes from 99 to 00 -- so, if you turn your computer off after you reset the clock back to 12-31-1999 23:59, it will say 01-04-1980 again when you turn it back on. Which is why you must leave it on this time.)

10. Leap Year Tests: Now set the date to 2-29-2000 and any time. Power off the computer and power it back on. It should still say Tue 02-29-2000, since 2000 is a leap year. Double check that the day of the week is Tuesday.

11. Verify that 3-1-2000 is a Wednesday by repeating the previous step.

12. You can optionally verify that it knows that 2000 contains 366 days, not 365.

  1. Verify that 12-30-2000 is a Saturday.
  2. Verify that 12-31-2000 is a Sunday.
  3. Verify that 1-1-2001 is a Monday.
13. When you are done testing, do not forget to reset your computer to today's correct, current, date and time.
  1. From the "A:\>" prompt of the floppy system, use the date and time commands to set the current date and time.
  2. Power off the computer.
  3. Remove the boot disk from the floppy drive.
  4. Turn the power back on and reboot your normal system.
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More PC Testing Links
  Much more detailed information about this problem: Michigan State University PC Test
If you prefer a program to test your PC: RighTime's Test2000

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This page last updated 2001-12-21. Please send comments and reports of broken links to the author: Roger Deschner

2001-12-21  ACCC Documentation
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