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Microsoft Year 2000 Readiness Disclosure & Resource Center |
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Windows Operating System Interactions with BIOS and Real Time Clock |
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3. Executive Summary
This paper addresses the interaction of the computer's Real Time Clock (RTC) and basic input/output system (BIOS) with the following Microsoft® operating systems: Windows NT® version 3.51, Windows NT® version 4.0, Windows® 98, Windows® 95, Windows® 3.x, and MS-DOS® version 5.x or later.
Use the easy-to-follow steps included in this paper to check the Year 2000 readiness of your PC's RTC/BIOS and operating system.
Most RTC rollover issues are remedied by the PC’s BIOS. However in older PCs, the BIOS software may not roll over automatically to 2000. In most of those cases, the century register in the RTC will remain at "19" when the date should roll from 1999 to 2000. An easy workaround for Windows users is to reset the date in Control Panel. The machine's BIOS and operating system should then maintain the date properly.
When the Windows® NT operating system starts up, it directly accesses the RTC’s memory and uses its time and date values to set the system time and date. Whenever Windows NT reads dates between 1900 and 1919 in the RTC it adds 100 to the year. In effect, it maps the time period forward to 2000 – 2019. Windows NT does not add 100 to dates between 1921 and 1999.
Logic built into the Windows® 98 operating system will automatically set the date forward at boot time if the BIOS does not roll over the RTC to 2000. The system does not automatically compensate for BIOSes that change valid dates.
Users of Windows 95, Windows 3.x, and MS-DOS version 5.x or later can address most rollover errors by simply resetting the date in Control Panel or by using the DATE command in MS-DOS.
Microsoft recommends that customers carefully evaluate their systems and test their computing environment from end to end to address overall Year 2000 issues.
Many manufacturers have developed products to help users deal with RTC/BIOS issues and the Year 2000. Select "BIOS" in the Year 2000 Tools section located at http://www.microsoft.com/technet/year2k/tools/tools.htm for links to third party suppliers. Microsoft has not tested, and makes no warranties concerning, any third-party products or resources such as those listed above.
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