In article . com,
wrote:

Why do the battery powered clocks in personal computers tend to keep
worse time than quartz watches, even the $1 ones?

The computer batteries measure fine, at least 3.15V.

I thought that the problem was temperature swings in the computers
(25-38C), but a couple of cheapo watches taped inside the computers
kept better time.


Dunno if it's still true in PC-land - I've been living in a Mac world
for a LONG time now - but when I was playing with them years ago, the
battery-backed real-time clock was read once at startup to set the
computer's software clock, which then kept time by counting clock
interrupts generated by the motherboard timing circuitry. That
interrupt, like any other "not non-maskable" interrupt, can be blocked
out for various reasons by various things, causing the software clock to
lose time. Usually, the amount of "lost" time isn't really noticable
except on "continuously on" machines. But with long periods between
restarts, heavy use of software (or firmware... The blame may not be in
your clock, but in your ROM code) that disables interrupts often or for
extended periods, and/or no intervention (be it human or software)
happening, it can grow to substantial amounts of time surprisingly quick.

Immediately after startup, the clock SHOULD be reasonably close to
right, since it will have been freshly set from the battery powered
clock, but after a while, it *WILL* go wonky unless steps are taken to
correct the drift - It's just the nature of the beast.

--
Don Bruder - - If your "From:" address isn't on my whitelist,
or the subject of the message doesn't contain the exact text "PopperAndShadow"
somewhere, any message sent to this address will go in the garbage without my
ever knowing it arrived. Sorry... http://www.sonic.net/~dakidd for more info