MITRE - Y2K - Other Dates of Concern

The following Y2K material has been kept available by MITRE for historical purposes only and has not been updated unless noted.

Other Dates of Concern

Source: Sandler, Robert J., February 29, 1996, THE YEAR 2000 FAQ: FREQUENTLY ASKED QUESTIONS ABOUT THE YEAR 2000 COMPUTER CRISIS, Version 2.1, Section 5.6.

What are some important programming future dates for DOS system designers besides 1999 and 2000? I'm doing these calculations quickly so I may be off by one.

1. DOS "Days-Since-1900"

Many DOS programs maintain the date as days--since-01-01-1900. This requires an unsigned 16-bit integer. (There were a few variants of this method, e.g., to have zero fall on a Sunday to simplify day-of-week calculations.)

Signed vs. unsigned:

19 September 1989: programmers who failed to specify "unsigned" 16-bit integers had their dates suddenly change to early in the 19th Century.

07 Jun 2079: 16-bit counters will roll over.

2. DOS File System Times

DOS has historically maintained the date in a packed integer field. It allocated 7 bits to the year field, starting in 1980.

01 Jan 2044: poorly written code may have problems with date if bit extraction is done improperly.

01 Jan 2108: rollover

PC Internal Clock and BIOS	Desktop PC Resolution	Clock/BIOS Flowchart	Appropriate BIOS Upgrade	Test Your PC System Clock	Testing Leap Year
Other Dates of Concern	FlashBIOS Upgrades	Testing Utilities & Patches	Vendor Patches & SW Libraries	Manual Clock Setting	PC Suppliers Compliance Lists

For further information directly related to Year 2000 issues, please contact Year2000@mitre.org