On Tue, 2007-03-06 at 12:27 -0800, John H. Robinson, IV wrote: > Andrew Lentvorski wrote:
> > > I believe that most things actually query the hardware clock when > > asked for time of day. > > Nope. The hardware clock is just as bad. In cheap consumer grade systems the hardware clock can't maintain accuracy. Our embedded systems lose and gain time as temperature changes, and they are temp. adjusted and have relatively good crystals in them. To have a very accurate clock would raise the system price significantly. > > -john > > [EMAIL PROTECTED]:~]% man hwclock | grep -A1 -B4 DOS > The System Time is the time that matters. The Hardware Clock's basic > purpose in a Linux system is to keep time when Linux is not running. > You initialize the System Time to the time from the Hardware Clock > when Linux starts up, and then never use the Hardware Clock again. > Note that in DOS, for which ISA was designed, the Hardware Clock is > the only real time clock. > > Which again is why it is important to use NTP if you care about having accurate system time. The problem with NTP is it can fail to adjust the time if the hardware clock is too far out of sync with reality (or if the server(s) can't be reached). A dead battery in a system can wreak havoc with keeping accurate time as the HW clock would be reset at every power cycle and NTP may not be able to cope with it. PGA -- Paul G. Allen BSIT/SE Owner/Sr. Engineer Random Logic Consulting www.randomlogic.com -- [email protected] http://www.kernel-panic.org/cgi-bin/mailman/listinfo/kplug-list
