Windows Time Service Technical Reference

Applies To: Windows Server 2003, Windows Server 2003 R2, Windows Server 2003 with SP1, Windows Server 2003 with SP2, Windows Server 2008, Windows Server 2008 Foundation, Windows Server 2008 R2, Windows Server 2008 R2 Foundation


Windows Time Service Technical Reference

In this guide


In Windows Server® 2003 and Microsoft Windows 2000 Server, the directory service is named Active Directory® directory service. In Windows Server 2008 R2 and Windows Server 2008, the directory service is named Active Directory Domain Services (AD DS). The rest of this topic refers to AD DS, but the information is also applicable to Active Directory.

The Windows® Time service, also known as W32Time, synchronizes the date and time for all computers running in an AD DS domain. Time synchronization is critical for the proper operation of many Windows services and line-of-business applications. The Windows Time service uses the Network Time Protocol (NTP) to synchronize computer clocks on the network so that an accurate clock value, or time stamp, can be assigned to network validation and resource access requests. The service integrates NTP and time providers, making it a reliable and scalable time service for enterprise administrators.


The W32Time service is not a full-featured NTP solution that meets time-sensitive application needs and is not supported by Microsoft as such. For more information, see Microsoft Knowledge Base article 939322, Support boundary to configure the Windows Time service for high-accuracy environments (

Where to Find Windows Time Service Configuration Information

This guide does not discuss configuring the Windows Time service. There are several different topics on Microsoft TechNet and in the Microsoft Knowledge Base that do explain procedures for configuring the Windows Time service. If you require configuration information, the following topics should help you locate the appropriate information.

What is the Windows Time Service?

The Windows Time service (W32Time) provides network clock synchronization for computers without the need for extensive configuration.

The Windows Time service is essential to the successful operation of Kerberos version 5 authentication and, therefore, to AD DS-based authentication. Any Kerberos-aware application, including most security services, relies on time synchronization between the computers that are participating in the authentication request. AD DS domain controllers must also have synchronized clocks to help to ensure accurate data replication.

The Windows Time service is implemented in a dynamic link library called W32Time.dll. W32Time.dll is installed by default in the %Systemroot%\System32 folder during operating system setup and installation.

W32Time.dll was originally developed for Windows 2000 Server to support a specification by the Kerberos V5 authentication protocol that required clocks on a network to be synchronized. Starting with Windows Server 2003, W32Time.dll provided increased accuracy in network clock synchronization over the Windows 2000 Server operating system and, in addition, supported a variety of hardware devices and network time protocols by means of time providers. Although originally designed to provide clock synchronization for Kerberos authentication, many current applications use timestamps to ensure transactional consistency, to record the time of important events, and other business-critical, time-sensitive information. These applications benefit from time synchronization between computers that is provided by the Windows Time service.

Importance of Time Protocols

Time protocols communicate between two computers to exchange time information and then use that information to synchronize their clocks. With the Windows Time service time protocol, a client requests time information from a server and synchronizes its clock based on the information that is received.

The Windows Time service uses NTP to help synchronize time across a network. NTP is an Internet time protocol that includes the discipline algorithms necessary for synchronizing clocks. NTP is a more accurate time protocol than the Simple Network Time Protocol (SNTP) that is used in some versions of Windows; however, W32Time continues to support SNTP to enable backward compatibility with computers running SNTP-based time services such as Windows 2000.

See Also


How the Windows Time Service Works Windows Time Service Tools and Settings

Other Resources

Microsoft Knowledge Base article 902229 Videos about the Windows Time Service