<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN"> <HTML ><HEAD ><TITLE >Computer Global Date and Time Concept</TITLE ><META NAME="GENERATOR" CONTENT="Modular DocBook HTML Stylesheet Version 1.7"><LINK REL="HOME" TITLE="Managing Accurate Date and Time" HREF="index.html"><LINK REL="PREVIOUS" TITLE="Why do We Need a Precise Clock?" HREF="why.html"><LINK REL="NEXT" TITLE="What are Time Zones?" HREF="tz.html"></HEAD ><BODY CLASS="section" BGCOLOR="#FFFFFF" TEXT="#000000" LINK="#0000FF" VLINK="#840084" ALINK="#0000FF" ><DIV CLASS="NAVHEADER" ><TABLE SUMMARY="Header navigation table" WIDTH="100%" BORDER="0" CELLPADDING="0" CELLSPACING="0" ><TR ><TH COLSPAN="3" ALIGN="center" >Managing Accurate Date and Time</TH ></TR ><TR ><TD WIDTH="10%" ALIGN="left" VALIGN="bottom" ><A HREF="why.html" ACCESSKEY="P" >Prev</A ></TD ><TD WIDTH="80%" ALIGN="center" VALIGN="bottom" ></TD ><TD WIDTH="10%" ALIGN="right" VALIGN="bottom" ><A HREF="tz.html" ACCESSKEY="N" >Next</A ></TD ></TR ></TABLE ><HR ALIGN="LEFT" WIDTH="100%"></DIV ><DIV CLASS="section" ><H1 CLASS="section" ><A NAME="time" ></A >2. Computer Global Date and Time Concept</H1 ><P >To determine the current time for some planet region, a computer needs exactly this two informations:</P ><P ></P ><OL TYPE="1" ><LI ><P >Correct <SPAN CLASS="acronym" >UTC</SPAN > (universal time as in Greenwich, but not <SPAN CLASS="acronym" >GMT</SPAN >) time</P ></LI ><LI ><P >Region's current Time Zone</P ></LI ></OL ><P >For computers, there is also the hardware clock, which is used as a base by the OS to set its time.</P ><P >OS date and time (we'll use only date <EM >or</EM > time from now on) is set on boot, by some script that reads the hardware clock, makes Time Zone calculations (there is no time zone data stored in <SPAN CLASS="acronym" >BIOS</SPAN >) and sets the OS. After this synchronization, <SPAN CLASS="acronym" >BIOS</SPAN > and OS time are independent from each other. So after a while they may have some seconds of difference. Which one is correct? If you don't make special configurations, none of them.</P ><P >We'll discuss here how to make them both <EM >globally 100% accurate</EM >.</P ></DIV ><DIV CLASS="NAVFOOTER" ><HR ALIGN="LEFT" WIDTH="100%"><TABLE SUMMARY="Footer navigation table" WIDTH="100%" BORDER="0" CELLPADDING="0" CELLSPACING="0" ><TR ><TD WIDTH="33%" ALIGN="left" VALIGN="top" ><A HREF="why.html" ACCESSKEY="P" >Prev</A ></TD ><TD WIDTH="34%" ALIGN="center" VALIGN="top" ><A HREF="index.html" ACCESSKEY="H" >Home</A ></TD ><TD WIDTH="33%" ALIGN="right" VALIGN="top" ><A HREF="tz.html" ACCESSKEY="N" >Next</A ></TD ></TR ><TR ><TD WIDTH="33%" ALIGN="left" VALIGN="top" >Why do We Need a Precise Clock?</TD ><TD WIDTH="34%" ALIGN="center" VALIGN="top" > </TD ><TD WIDTH="33%" ALIGN="right" VALIGN="top" >What are Time Zones?</TD ></TR ></TABLE ></DIV ></BODY ></HTML >