time sources : Java Glossary

2008-03-09 by Roedy Green ©1996-2008 Canadian Mind Products
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time sources

In our technological world there are many ways you can get the current time and date. Here is an eclectic list of time sources:

From GPS satellites. GPS provides a most excellent time source since it naturally compensates for propagation delay and is immune to network congestion and weather.
SetClock is a Java Applet you can run on your PC. It will get the accurate time from an atomic clock on the web.
From an atomic clock timeserver on the web using NTP (Network Time Protocol). Timeservers come is various grades of accuracy. You are not supposed to pester the very accurate ones. They are for the secondary servers. Here is list of them.
Last revised: 2000-01-01
java.lang.System.currentTimeMillis () will give you the time in milliseconds since 1970 Jan 1 0:00 GMT. This is your best bet for computing elapsed times. Freshly minted java.util.Date objects contain the current GMT date/time stamp as do freshly minted java.util. GregorianCalendar objects.
Time.gov is a government website that will give you local time.
From Windows Vista which gets it from a Microsoft timeserver, time.windows.com. It is quite unreliable, so I suggest replacing it with another.
From the NIST WWVB radio signal broadcast from Fort Collins, Colorado. This is how high tech wall clocks and wrist watches maintain perfect time and know when to flip back and forth to daylight savings. They are called analog atomic clocks and digital atomic clocks, though there is nothing radioactive in them. They are merely radio-synchronised from a government atomic clock.
radio-synched clocks for more details and information on where to buy them
From a signal PBS embeds in its TV broadcasts. This is how VCRs can get the time automatically.
From the CBC radio time signal each day at 10 AM on the FM broadcast stations.
From a signal broadcast on the AC power, put here by the utility company.
From your TV Station broadcast channel guide.

atomic clock
benchmark
Calendar
Date
daylight saving time
GMT
gotchas for extensive hints on date/time processing
leap second
longitude
Microsoft File Times
mixed base
NTP
OpenType
Pentium RDTSC high resolution timer
profiler
radio-synched clock
RDTSC: coding an RDTSC access in assembler
SetClock
SI prefixes such as pico and femto
sleep
TAI
time
Timer
timestamp
UTC
wall clock
Windows Vista

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