The time zone identifier is a key string that uniquely identifies a particular time zone. In Windows XP and Windows Vista, it corresponds to the subkeys of the HKEY_LOCAL_MACHINE\Software\Microsoft\Windows NT\CurrentVersion\Time Zone branch of the registry. It can be passed as a parameter to the FindSystemTimeZoneById method to retrieve a particular time zone from the registry.

Important Note:
If you are defining a custom time zone, you should not assign it an identifier longer than 32 characters because this is the maximum length supported by the Windows registry.

The value of the Id property is usually, but not always, identical to that of the StandardName property. The identifier of the Coordinated Universal Time zone is UTC.

The following example lists the identifier of each of the time zones defined on the local computer.

Dim zones As ReadOnlyCollection(Of TimeZoneInfo) = TimeZoneInfo.GetSystemTimeZones()
Console.WriteLine("The local system has the following {0} time zones", zones.Count)
For Each zone As TimeZoneInfo In zones
   Console.WriteLine(zone.Id)
Next

ReadOnlyCollection<TimeZoneInfo> zones = TimeZoneInfo.GetSystemTimeZones();
Console.WriteLine("The local system has the following {0} time zones", zones.Count);
foreach (TimeZoneInfo zone in zones)
   Console.WriteLine(zone.Id);

Windows 7, Windows Vista, Windows XP SP2, Windows Server 2008 R2, Windows Server 2008, Windows Server 2003

.NET Framework

Reference