Changing Your Operating System's Default Date Format To Use Four-Digit Years

How to change your OS's default date format
Advantages of changing your OS's default date format
Limitations of changing your OS's default date format
Disadvantages of changing your OS's default date format

Related documents

Why You Should Enter Dates With Four-Digit Years Whenever Possible
Standards for Representing Dates
DateWise, Ltd.'s Short Date Format
Microsoft Corporation's Windows 95, Windows 98 and Windows NT Year 2000 e-mail hoax

The format for displaying dates in most personal computer operating systems, such as Windows 95 and the Mac OS, is set "at the factory" to use two-digit years, such as "05/13/29".

Dates containing two-digit years are century-ambiguous. For instance, the date "05/13/29" could reasonably be interpreted either as "May 13, 1929" or "May 13, 2029". For this reason, it is desirable to change your operating system's default date format to use full, four-digit years. Here's why:

Many of your application programs, such as spreadsheet and database programs, are programmed to use the same format that your operating system uses when displaying dates. If your operating system is set to display dates with two-digit years, many application programs will also display dates with century-ambiguous two-digit years.

Merely having your programs display dates with two-digit years isn't in itself problematic, in a Y2K context or otherwise. However, this can lead to two types of subtle problems that you might first encounter when the year 2000 arrives or when your programs first begin using dates from the 21st century:

• Making data entry validation more difficult. If your programs display dates with only two-digit years, this makes it more difficult to visually validate that dates you've entered with two-digit years have automatically been assigned to the correct century by your programs.
  
  If you enter "05/13/29" into a spreadsheet cell or a database field, and this date is displayed with just a two-digit year, once again as "05/13/29", you can't readily see whether your program has interpreted that date as "05/13/1929" or "05/13/2029".
  
  
• Causing century-ambiguous two-digit dates to be exported to text files or the Clipboard. When some of your programs display dates with only two-digit years, they will also use this format when exporting data via text files or the Clipboard. This could lead to century-ambiguous dates with two-digit years being exported to other programs.
  
  Such dates could actually change centuries as a result of being exchanged between two different programs.

In addition, if your operating system's date format uses two-digit years, this can lead to a third type of subtle problem:

• Restricting you to entering dates with only two-digit years. A few applications use your OS's date format within their data entry routines. If your OS's date format uses two-digit years, these applications may restrict you to only entering dates with two-digit years, thus limiting the possible range of dates which you can enter.

For this reason, it is often desirable to change your operating system's default short date format so that dates will be displayed with clear and unambiguous four-digit years, such as "05/13/2029" or "2029-05-13". We expect that most personal computer users affiliated with the UC Berkeley campus will benefit by changing their operating systems' default date format to use four-digit years.

However, doing so is not a panacea that will automatically correct a vast array of Y2K problems through a single click of the mouse. Rather, the effects of making this change are often quite modest. In addition, you might potentially encounter problems in the operation of a few application programs and with certain methods of sharing data after changing your OS to use a four-digit year format. Making this change could also lead to formatting problems - display or printing anomalies - in some data files. The limitations and disadvantages of making this change, as well as its advantages, are discussed below.

How to change your OS's default date format

The steps you can take to change your operating system's default date format to use four-digit years will depend on which OS you're using. These are presented in a number of the platform-specific Y2K Readiness Checklists elsewhere on this Web site, including:

• Macintoshes
  
  
• PCs running Windows 3.1x
  
  
• PCs running Windows 95
  
  
• PCs running Windows 98
  
  
• PCs running Windows NT 3.5.1
  
  
• PCs running Windows NT 4.0

On the Berkeley campus (and presumably elsewhere in the USA), you might typically change your OS's default date format from "mm/dd/yy" to "mm/dd/yyyy". (In this format, "mm" represents the month, "dd" the day, and "yyyy" the full, four-digit year, including the century.) An alternative might be to switch to the international and US standard for representing dates, "yyyy-mm-dd". See Standards for Representing Dates for a discussion of these two date formats.

Advantages of changing your OS's default date format

Some of the specific advantages of making this change include:

Causing your application programs to display dates with four-digit years

When you change your operating system's default date format to display four-digit years, some applications will also automatically use that format when displaying dates.

Why is this important? Depending on how your various application programs work, you might thus see such desirable effects as:

• Making it easier to check how dates entered with two-digit years are interpreted.
  
  When you enter dates with century-ambiguous two-digit years, such as "05/13/29", many application programs use a set of rules to interpret such dates as falling into either the 20th or 21st centuries, such as (in this example) either "May 13, 1929" or "May 13, 2029". By changing your operating system's default date format to use four-digit years, some applications will immediately display dates - right after you enter them - with full, four-digit years. As a result, you can see how your program has interpreted any dates you entered with two-digit years, and readily correct any dates which your program might have assigned to the "wrong" century.
  
  This change - in and of itself - has compelled some institutions to adopt a four-digit year date standard on all of their distributed computers.
  
  (To avoid such problems altogether, it's a much better idea to always enter dates with full, four-digit years into your programs.)
  
  
• Preventing dates from changing centuries when data is exported from one program and imported into another program.
  
  Some programs export data - via such methods such as the Clipboard or comma- or tab-delimited text files - using the same format in which this data is displayed onscreen. As noted in Data Sharing Methods: Finding & Resolving Y2K Problems , if your programs display dates with two-digit years, they may also export dates with two-digit years. Such dates are century-ambiguous, and upon being imported by another program, could be interpreted as falling into a different century. Thus, dates could literally be changed from the 20th to the 21st century, or vice versa, merely as a result of having been exported by one program and imported into a different program.
  
  Changing your operating system's default date format to use four-digit years will cause many application programs to display dates with four-digit years. As a result, in many cases, these programs will also export data copied to the Clipboard or saved to text files with dates containing unambiguous four-digit years. These dates would no longer be at significant risk of being reassigned to the 'wrong' century when they are exported by one program and then imported by another program.
  
  Note that, as described below, after changing your operating system settings to use short dates with four-digit years, some of your application programs (such as Microsoft Excel) may display newly-entered dates with full, four-digit years, but will still display (and hence export) previously-entered dates with two-digit years.

Allowing a few application programs to accept dates entered with four-digit years

In the case of a few application programs, if you wish to enter dates with full, four-digit years, you must change your operating system's default date format to use four-digit years. If you don't make this change, you will be limited to entering dates with only two-digit years.

This problem can manifest itself in several ways. For example, with certain programs, this might restrict you to entering only dates between 1900 through 1999, or only dates which fall within a different 100-year "window" defined by your program, such as from 1950 to 2049. With some other programs, it might constrain you to entering only only two year digits into date input fields, even if these fields are formatted to display dates with full, four-digit years.

Two examples:

• According to Apple Computer, Inc.'s Tech Info Library article AppleWorks/ClarisWorks: Entering Year 2000 & Beyond Dates , you'll need to change your operating system's settings "to a date style that includes all four digits of the year" in order to enter a full range of 20th and 21st century dates in ClarisWorks 4.0 for Windows or for the Mac OS. (ClarisWorks for the Mac OS was recently renamed to AppleWorks.)
  
  
• According to a Lotus Development Corporation Customer Support Technote, Unable to Enter Four Digits for Year , both Approach 97 Edition and Approach 96 Edition for Windows 95 require that Windows' Regional Settings date display format be changed to a four-digit year format in order to avoid a problem where, "when attempting to enter dates with four digit years, [a date] field [which displays a four digit year] only accepts the first two digits."
  
  (If the link above should be changed or otherwise fails to work, you can also locate this Technote via DateWise, Ltd.'s handy Approach for Windows page.)

Causing your operating system to display dates with four-digit years

After making this change, your operating system will begin displaying four-digit years in certain places it may have previously displayed two-digit years. For example, your OS may begin using four-digit years when listing the dates that your files were last modified. This may make it easier to identify files created in the year 2000 and beyond.

Limitations of changing your OS's default date format

After making this change, you may not see any change in behavior on the part of some application programs. This is because some of your programs may not use your operating system's default date format. And even some programs which do use this date format may not always use it in every situation where they handle dates.

In addition, changing your OS's default date format to use four-digit years, in itself, is only a partial solution to the problem of century-ambiguous dates. Regardless of the OS date format being used, you'll ideally need to follow the practice of entering dates with four-digit years into your documents. You'll also need to coordinate with those with whom you share data, so that both you and they agree to exchange dates with unambiguous four-digit years.

Disadvantages of changing your OS's default date format

The potential disadvantages of changing your OS's default date format to use four-digit years primarily concern a relatively small number of application programs, both custom and off-the-shelf, which may exhibit problematic behavior after you make this change. Some examples include:

Problems in the operations of some application programs

• Changes in program behavior when dates with two-digit years are entered.
  
  After changing your OS's default date format to use dates with four-digit years, a few application programs may start behaving differently - and problematically - when you enter dates with two-digit years.
  
  For example, after changing the default date format in recent versions of Microsoft Windows (such as Windows 95 and NT 4.0) to use four-digit years, the Lotus 1-2-3 97 spreadsheet program will start interpreting the "/" date separator as a division symbol when you subsequently enter dates using only two-digit years. Lotus 1-2-3 would then interpret the date "05/13/29" as "5 divided by 13 divided by 29". The workaround - if you happen to be using this application - is to always enter dates with four-digit years.
  
  After making this same change to Windows' default date format, Microsoft's calendaring program, Schedule+ 95/7.0x for Windows, will initially display two-digit years padded with leading zeros, which could be disconcerting for some users. For instance, if you enter the two-digit year "23," Schedule+ will initially display that date as "0023".
  
  However, when you press the Tab key to leave that field, Schedule+ will immediately convert the two-digit year into a four-digit year (using its own internal conversion rules), and then display the full, four-digit year.
  
  
• Other types of operational problems.
  
  A few application programs may be programmed to recognize and use your operating system's default date format, but due to flaws in their programming logic, they may exhibit other types of problematic behavior once you've changed this format to use four-digit years.
  
  These problems appear to be most prevalent in custom-written programs, and in "vertical market" programs specific to certain industries or fields, although it is conceivable they might also occur in other, more widely-used types of programs.
  
  As an example, we've seen a second-hand report claiming that an accounting application "failed to load" after the OS's date display format was changed. And two second-hand reports both noted that, in messages posted to a forum sponsored by a non-profit Year 2000 information clearinghouse, Rx2000 , certain medical industry-specific applications were identified as having problems after this change was made. (We don't currently have any details regarding what types of problems were encountered.)
  
  If you use a critical application program, it is important that you check with your vendor and/or perform careful testing to be certain that changing your OS's date display format will not adversely impact that program's operation.

Problems affecting programs and scripts which handle dates as text strings

Some programming, scripting, or macro languages have built-in functions which can return dates as text strings. When your OS's default short date format is changed, these functions may return "mm/dd/yyyy" strings (or whatever new OS date format you've selected) rather than "mm/dd/yy" strings (or whatever format was in use before).

This may mean that programs or scripts that rely on the length of these text strings or the position of the year within these strings may fail in a variety of ways. We expect that this problem will be most likely to affect casual, user-written programs and scripts, although it could also affect at least a few custom-written applications.

Problems when sharing data

When sharing data via the Clipboard, text files, or other methods, with some application programs, dates in your "exported" data may now contain four-digit years. If the programs with which you are sharing this data are not prepared for this change, they may behave incorrectly when trying to import or process this data.

Problems in display and printing

• Inconsistent display of dates within your documents.
  
  With some application programs, such as recent versions of Microsoft Excel, when you switch to a date format using four-digit years, then enter dates into your existing documents, you may find that the display formats for previously entered dates remain static; they are not automatically changed to the new format. As a result, your previously-entered dates may still be displayed using two-digit years, while newly-entered dates are displayed using four-digit years.
  
  In addition, any dates to which custom formats had been applied will not be automatically changed to use the new four-digit display format specified by the operating system.
  
  If you need these formats to be consistent, you may need to select the previously entered dates and change their display format to the new, four-digit year format.
  
  
• "Longer" dates causing display or printing anomalies.
  
  Since displayed dates in some applications will be made longer - from two year digits to four - you could encounter some display or printing anomalies:
  
  
  • Some data entry or display fields of fixed size may now incorrectly display dates in existing records. For example, after you've expanded the display of dates like "05/13/29" to "05/13/2029", a fixed-width eight character display field might now display only the first eight characters of the date, such as "05/13/20".
    
    If your program inconsistently stores and/or displays previously entered and newly-entered dates (see above), it is also possible that you'll see only newly-entered dates as incorrectly displayed.
    
    
  • Unless widened, date values in some spreadsheet columns might be displayed as truncated, or their contents may instead be displayed as all hashes ("###") or asterisks ("***"). You'll need to widen these columns to display their contents, which could potentially cause minor problems when formatting your spreadsheet for printing.
    
    
  • Some printed reports might potentially now overprint the new longer dates on top of other text, "bump" other report text further over in order to make room for these longer dates, inappropriately "wrap" long lines, or otherwise mis-position dates.