Some Computer Hints

Windows - Daylight Saving Time Adjustment

(For Very Old Versions Of Windows)

In most European countries, the day of switching from daylight saving time (DST) to normal time has changed. Before 1996, this was done on the last Sunday of September. However, since 1996, this is being done on the last Sunday of October. Some Windows versions still adjust the clock on the last Sunday of September. To correct this, some modifications in the Windows registry need to be done.

Below I give a procedure of how to do this for the time zone used in Turkey. Time zone for Turkey is specified by selecting “(GMT+02:00) Athens, Helsinki, Istanbul” and checking the “Automatically adjust clock for daylight saving changes” checkbox in the Time Zone tab of Date/Time Properties applet in Windows 95 Control Panel.

To shift the last day of DST from September to October you need to modify the binary value of key TZI in the

  • Windows\CurrentVersion\Time Zones\GFT (for Windows 95) or
  • Windows NT\CurrentVersion\Time Zones\GFT Standard Time (for Windows NT 4.0)

sub-branch of your HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\ Registry branch as follows:


0000   88 FF FF FF 00 00 00 00
0008   C4 FF FF FF 00 00 0A 00
0010   00 00 05 00 03 00 00 00
0018   00 00 00 00 00 00 03 00
0020   00 00 05 00 02 00 00 00
0028   00 00 00 00

For reference, I give the exported list of all the keys in the related branch of my (Windows 95) registry below:

[HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Time Zones\GFT]
"Display"="(GMT+02:00) Athens, Helsinki, Istanbul"
"Dlt"="GFT Daylight Time"
"Std"="GFT Standard Time"

After you do the registry update, you will need to reboot your computer and reselect the modified time zone from the Control Panel’s Date/Time application to make sure that your computer works properly and the changes took effect. You can test the change by running a Perl script given in my Perl Script - Daylight Saving Time Check page.

Note that, the for the years before 1996, the day of switching from DST to normal time should be last Sunday of September and not of October; however as far as I know, there is no way to specify such historical (past or future) time zone information in the Windows registry.