Computer time synchronisation is highly important in modern computer networks, precision and time synchronization is critical in many applications, particularly time sensitive transactions. Just imagine buying an airline seat only to be told at the airport that the ticket was sold twice because it was purchased afterwards on a computer that had a slower clock!

Modern computers do have internal clocks called Real Time Clock chips (RTC) that provide time and date information. These chips are battery backed so that even during power outages, they can maintain time but personal computers are not designed to be perfect clocks. Their design has been optimized for mass production and low-cost rather than maintaining accurate time.

For many applications, this is can be quite adequate, although, quite often machines need time to be synchronised with other PC's on a network and when computers are out of sync with each other problems can arise such as sharing network files or in some environments even fraud!

Microsoft Windows (2000 and above) has a time synchronisation utility built into the operating system called Windows Time (w32time.exe) which can be configured to operate as a network time server. It can be configured to both synchronise a network using the internal clock or an external time source.

Note: Microsoft strongly recommends that you configure a time server with a hardware source rather than from the internet where there is no authentication.

To configure Windows Time service to use the internal hardware clock, first check that w32time is located in the system services list in the registry, to check:
Click Start, Run then type regedit then click ok.
Locate and then click the following registry entry:
HKEY_LOCAL_MACHINESYSTEMCurrentControlSetServicesW32Time

It is highly recommended that you back up the registry as serious problems may occur if you modify the registry incorrectly, modifications to the registry are done at your own risk.

Note: the following instructions are based on Windows 2000 other versions of Windows may differ.

To begin configuration for an internal clock, click on the following subkey:
HKEY_LOCAL_MACHINESYSTEMCurrentControlSetServicesW32TimeParameters
In the right pane, right-click ReliableTimeSource, then click Modify.
In Edit DWORD Value, type 1 in the Value Data box, then click OK
Exit Registry Editor

To restart the Windows Time Service click Start, Run (or alternatively use the Command Prompt facility).
Type: net stop w32time && net start w32time
Then press enter.

To reset the local computers' time, type the following on all computers except for the time server which must not be synchronised with itself:
w32tm -s

To configure the Windows Time service to use an external time source, click Start, Run and type regedit then click OK.

Locate the following subkey:
HKEY_LOCAL_MACHINESYSTEMCurrentControlSetServicesW32TimeParameters
In the right pane, right-click Type then click Modify, in edit Value type NTP in the Value data box then click OK.

Now in the right pane, right click ReliableTimeSource, then click Modify.
In the Edit DWORD Value box, under Value Data, type 0, then click OK.

Right-click NtpServer in the right pane then click Modify.
In Edit Value, type the Domain Name System (DNS), each DNS must be unique.
Now click Ok.

For Windows 2000 Service Pack 4 only, set the time correction settings to do this locate:
HKEY_LOCAL_MACHINESYSTEMCurrentControlSetServicesW32TimeParameters
In the right pane, right-click MaxAllowedClockErrInSecs, then Modify in the Edit DWORD Value box, , type a time in seconds max number of seconds difference between the local clock and the time received from the NTP server in order to be considered a valid new time.
Click OK.

To set the poll intervals locate:
HKEY_LOCAL_MACHINESYSTEMCurrentControlSetServicesW32TimeParameters
In the right pane, right-click Period, then click Modify.
In the Edit DWORD Value box, under Value Data, type 24 then OK
Exit Registry Editor

Click Start, then Run then type the following and press Enter:
Net stop w32time && net start w32time

To reset the local computers' time, type the following on all computers except for the time server which must not be synchronised with itself:

Network Time Protocol (NTP) is an Internet protocol used for the transfer of accurate time, providing time information along so that a precise time can be obtained

To enable the Network Time Protocol; NTPserver, locate and click:
HKEY_LOCAL_MACHINESYSTEMCurrentControlSetServicesW32TimeTimeProvidersNtpServer
In the right pane, right-click Enabled, then click Modify.
In the Edit DWord Value box, type 1 under Value data, then click OK.

Now go back and click on
HKEY_LOCAL_MACHINESYSTEMCurrentControlSetServicesW32TimeParametersNtpServer
In the right pane, right-click NtpServer, then Modify, in the Edit DWORD Value under Value Data type In the right pane, right-click NtpServer, then Modify, in the Edit DWORD Value under Value Data type the Domain Name System (DNS), each DNS must be unique and you must append 0x1 to the end of each DNS name otherwise changes will not take effect.
Now click Ok.

Locate and click the following
HKEY_LOCAL_MACHINESYSTEMCurrentControlSetServicesW32TimeTimeProvidersNtpClientSpecialPollInterval
In the right pane, right-click SpecialPollInterval, then click Modify.
In the Edit DWORD Value box, under Value Data, type the number of seconds you want for each poll, ie 900 will poll every 15 minutes, then click OK.

To configure the time correction settings, locate:
HKEY_LOCAL_MACHINESYSTEMCurrentControlSetServicesW32Timeconfig
In the right pane, right-click MaxPosPhaseCorrection, then Modify, in the Edit DWORD Value box, under Base, click Decimal, under Value Data, type a time in seconds such as 3600 (an hour) then click OK.

Now go back and click:
HKEY_LOCAL_MACHINESYSTEMCurrentControlSetServicesW32Timeconfig
In the right pane, right-click MaxNegPhaseCorrection, then Modify.
In the Edit DWORD box under base, click Decimal, under value data type the time in seconds you want to poll such as 3600 (polls in one hour)

Exit Registry Editor
Now to restart windows time service, click Start, Run (or alternatively use the command prompt facility) and type:
net stop w32time && net start w32time

And on each computer, other than the time server, type:
W32tm/ -s

And that's it your time server should be now up and running.