If there was an answer in this thread, I must have missed it. So many
ideas, so few applications of the facts :-)

There are two clocks in a PC (I don't know MACs) A hardware one, and the
software clock. When the PC boots, the BIOS reads the hardware clock, and
the OS asks the BIOS what time it is. From there on, good old windows or
whatever is doing the clock counting, using an interrupt timer. Given the
sloppy programming, and the inability of windows to pre-emptively
multitask, the software clock is not going to be very accurate. Just open
your time settings screen and watch the second hand on the clock. That
will show you right away that not only is windows terribly inefficient, it
is unable to update the clock consistently, and accurately, even when it
is 'idling,' due to system overhead, poorly implemented.

Each time you power down or restart the PC, the hardware clock is read,
and it is more accurate than the software, although still subject to
crappy crystals and poorly implemented devices. If you leave the computer
on for days at a time, a restart will probably get the clock back to a
more accurate setting, but not necessarily much better.

The question of why the PC clock is so inaccurate, and yet more expensive
than a cheapo watch is simply a matter of "how ya gonna get the
information out of the cheap watch, and into the PC?" The clock itself,
and the crystal are only a portion of the hardware required by a PC to
know what time it is. The additional requirements increase the sicon die
size, as well as the complexity of the design, so the higher cost is to be
expected. If you can get the time out of a cheap watch, in binary form, at
the proper levels, and the proper timing specs, without raising the price
of the $1 watch, a lot of people would like to hear from you ;-)

There are many sources of RTC boards that plug into a PCI slot and take
over the timekeeping for highly accurate applications, and of course, as
so many pointed out, apps the use the National Standards are free and easy
given net access.

Just another 3.5 cents.

Mark