Strata

• Layers of Accuracystacks of book image by Orlando Florin Rosu from Fotolia.com
  
  Servers are located in several places around the Internet. The servers are classified according to the strata, or layer of the clock. Stratum 0 are highly accurate atomic clocks and are directly connected to stratum 1 servers. Stratum 0 clocks are not available over a network. A stratum 1 server derives its time from a directly connected stratum 0 atomic clock. A stratum 2 server will derive its time from one or more stratum 1 servers. Most users will reference a stratum 1 or stratum 2. Although the theoretical maximum is stratum 256 clocks, clocks lower than stratum 8 never exist.
  
  

Client Software

• Clients request time.question mark image by Georgios Kollidas from Fotolia.com
  
  Client software is included in most operating systems including Linux, Macintosh and Windows. When configuring a clock on a computer, there is an option to set the date and time manually or to automatically keep the clock synchronized with Internet Time Servers. The client software then sends an NTP request to a server when the system starts up and at periodic intervals when the system is running.
  
  

Multiple Servers

• Multiple servers increase accuracy.Computer servers skyline image by patrimonio designs from Fotolia.com
  
  To increase accuracy, the computer might request the time from multiple servers or from peers. Using multiple servers allows the client to estimate the time more accurately by estimating the delay from several different servers. This also will allow the client to eliminate time from servers that are obviously wrong.
  
  

Accuracy

• Accuracy depends on the source.clock image by Stanisa Martinovic from Fotolia.com
  
  For most business applications, synchronization to within several seconds is sufficient. NTP easily can synchronize clocks to within one-tenth of a second over the Internet. For scientific applications where higher accuracy is required, a pulse-per-second source (PPS) is needed. The most common PPS source is GPS, or the Global Position System. A GPS receiver connected to a computer will tell the computer very accurately when a second starts. In combination with NTP the computer clock can be accurate within 50 microseconds or the real-time Internet Servers. A microsecond is one-millionth of a second.
  
  

Lists of Servers

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  Time Servers are located throughout the world. These are typically run by universities or by government research organizations. An company usually will have one computer use a stratum 1 server on the Internet and then become a stratum 2 server for all of the computers inside the company. For a list of time servers, see the Resources.