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Horse Sense #63
In this issue:
Y2K Returns: It is About Time!
Welcome to the new and improved
Daylight Savings Time! Are your computers giving you
the correct time? Now is the time to check. Any
Pre-Windows XP system is likely to have the wrong
time, for example. It would also be a good idea to
check your fax machines. Send an e mail to yourself.
Check the headers. Are the times correct? If you
need help with time, call Iron Horse!
Computers are very dependent upon
time. The rollover from 1999 to 2000 was especially
troublesome as any program or operating system using
two digit years would cause a real problem. Would 00
be 1900, 2000, or some other number when the
rollover happened? Would an "invalid" number shut
down the system, cause it to run in reverse, or
cause some other unpredictable action? It took a
massive effort worldwide to identify vulnerable
systems and correct them. Now, the US and other
countries are changing how they implement daylight
savings time. In case you haven't reset your clock
yet, it happened earlier this year and will end
later. If you want to read more about time in the
US, go to
www.time.gov. Not only will you see the current
time, but you will also be able to read all about
issues like Daylight Savings Time and how to fix
time issues.
There are other time related
issues that will be coming up. Some systems count
time from January 1, 1970 in seconds. For those
systems that do so and use a standard 4 byte integer
to do the counting, that means they can count up to
2 to the power of 31 seconds (there is one bit
reserved for a sign). That means that on Tuesday,
January 19 at 03:14:07 of the year 2038 equipment
prone to this bug will give the time as Friday,
December 13 20:45:52, 1901. Some programs that
calculate dates are already giving incorrect values.
Any date calculation using seconds since 1/1/1970
will give an incorrect result if the number exceeds
31 bits. If you averaged two dates together, for
example, you would start getting errors if your
dates were after January of 2004.
One of the most important
components of any computing device is its timing
crystal. Think of this as the drummer counting out
time for the computer. Every part of computer
performs its actions relative to that beat, like
other instruments in a band playing their part of a
piece of music. The timing crystal also counts
actual time in very small increments. So, in theory,
your computer is a very precise time keeping device.
Unfortunately, while your computer may be precise,
it often is not accurate. Besides issues like the
2038 bug, Y2K, and Daylight Savings Time, a computer
will slowly drift off of the correct time because of
small differences between the change in true time
and the time counted in the machine. For example,
over 30 days, a 1 second error in a day is 30
seconds. This represents a 0.001% error. As it turns
out, many computing devices will not keep time that
accurately.
Clocks do not know what time it
is unless you first set them. Even if you could set
multiple clocks to the same exact time, they will
drift away from the true value at varying rates.
This can cause huge problems as time can really be
money. For example, you sell one million shares of
stock at 10:17:22 AM by your computer clock, but by
your broker’s clock it was 10:18:27 AM and on the
exchange it was 10:18:13 AM. What if the price
changed in that time frame? Who is right? You also
want your time to be correct so that you can tell
when something happened or will happen. It could be
very difficult to fix a mail problem when a message
you sent seems to arrive 5 minutes before you sent
it.
To maintain accurate time, the
entire world agrees on a reference time called
Coordinated Universal Time (previously called
Greenwich Mean Time). Devices like atomic clocks are
used to deliver very precise reference Coordinated
Universal Time. Computers throughout the world
access servers synchronized to these time sources
through Network Time Protocol (NTP). NTP gets the
correct Coordinated Universal Time from a reference
time server. NTP also calculates how much time it
takes to get that answer and corrects for problem as
well. Reference time servers are graded on their
ability to provide "true" time. A stratum 1 NTP
server would be the closest to true time and is
directly tied to a very accurate timing device.
These servers tend to be very busy and their
operators do not want just anyone asking them for
the correct time. Many stratum 1 and even stratum 2
servers are not publicly available. In general, most
of us should be using stratum 3 or higher time
servers as our reference sources simply because we
don’t need that high a degree of time precision. A
few thousandths of a second will be just fine. It is
not necessary for every machine on your network to
get its time directly from a reference time server
on the Internet. Once you synchronize one machine on
your network to an external time source, you can
then have all the other machines on your network
match this internal time server. In addition, since
clients of the internal time server are most likely
in the same time zone, they can pick up that
information from the server as well.
If you think about it, time zones
are only useful to humans. Computers don't care what
time of day it is. On very large networks, one might
use Coordinated Universal Time for all the devices,
even if they are in different time zones. That way,
you could synchronize all your logging and graphing
so that events matched up around the world. Most of
us, however, want our devices on local time so that
when someone reports "This happened at 3 pm today,"
the technician can look at graphs or logs in local
time and see what they are talking about.
If you want to know more about
time or need help using time on your network, call
Iron Horse.
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