When I shut down my computer, should I turn off the power supply
switch on the rear of the computer every time?
I wouldn't have even thought of doing this, except I've noticed the
optical mouse stays lit if all I do is let Windows shut down the
computer.

Hi there gvg, thanks for writing us.

Most people view powering down the computer as a judgment call, it
depends what your goals are. I'll outline some of the reasons you may
or may not want to turn the computer off when shutting it down

1. Turning off not harmful --people used to think flipping the power
switch on and off was a bad idea. This is not true.

"Contrary to popular belief, turning on and off the computer doesn’t
shorten its life. As Lawrence Berkeley National Laboratory points out,
"The belief that frequent shutdowns [of PCs] are harmful persists from
the days when hard disks did not automatically park their heads when
shut off; frequent on-off cycling could damage such hard disks."
Lawrence Berkeley reassures us that, "Modern hard disks are not
significantly affected by frequent shut-downs. Shutting down computers
at night and on weekends saves significant energy without affecting
the performance." So, if you are going to be away from the computer
for several hours, turn it off."

http://www.nesea.org/buildings/info/eleventhings.html and
http://www.zdnet.com/products/stories/reviews/0,4161,914029,00.html

an alternative viewpoint is here:
http://www.smartcomputing.com/editorial/article.asp?article=articles%2F1998%2Fjul98%2F0714%2F0714%2Easp&guid=p4f7g5e0&searchtype=0&WordList=shutting+down

2. Saving energy -- you didn't mention if you had a laptop or a
desktop machine, but turning off even just the monitor of a desktop
machine can significantly save energy

"If a computer must be left on after-hours, turning off the monitor
will not affect the program that is running, but will save 75 per cent
of the total energy required to run the computer. These savings can be
compounded. Shutting down computers when not needed reduces heat
generation, which in turn cuts back the need for air conditioning."

http://www.bchydro.com/business/etools/news/4.html

3. the components get a chance to cool down

This is a double-edged sword because some people argue that the
heating and cooling cycles slightly weaken the connections between
components and so argue that the change it temperatures is more
important than the high temperatures. The people over at gen-x-pc.com
think this isn't true and that ultimately the decision is up to you.

http://www.gen-x-pc.com/general_questions.htm [scroll down on this
page]

4. RAM 

Turning your computer off gives your Random Access Memory a chance to
unfragment

"The memory (RAM) becomes fragmented with use. As you open and close
your favorite programs, little bits and pieces of your program stay in
RAM and are not completely eliminated when you close them. Eventually,
your 64 Megabytes (or whatever) of RAM becomes so "chopped up" that
you cannot open large programs or data files anymore, or they open
very slowly. We've seen computers that took about 30 seconds to a
minute to respond to the click of a mouse button. This delay time
would drop to about 2-3 seconds upon restarting the computer.  When
you restart your computer, the RAM is loaded with Windows 95/98/ME and
a few of the small programs that automatically start when you turn on
your computer. (You can see some of their icons in the System Tray
next to the Time in the lower right-hand corner of the screen.) The
rest of the RAM is free in a large, continuous block, allowing you to
load more of your important programs."

http://www.ezinstructions.com/leaveon.htm

So, I checked out a good chunk of web pages debating this issue and
they seem to generally say "while it's up to you, turning it off seems
to have more benefits." One thing that I do at home, with my several
computers, is to plug in all the peripherals for each computer
[monitor, computer, scanner, etc] into one surge protector, and then
turn off the surge protector, so everything is turned off at once.
Less wear and tear, a safer power supply, and no climbing under the
desk to reach the backs of all my things.

Here is an interesting forum debate over the optical mouse light on
"feature" that you have described

http://www.neoseeker.com/forums/index.php?fn=view_thread&t=1989

Hope this is helpful to you, thanks for writing.

jessamyn-ga

google search terms used

"turning your computer off" RAM
://www.google.com/search?num=30&hl=en&lr=&safe=off&q=%22turning+your+computer+off%22+RAM

"shutting down" versus "turning off" the computer
://www.google.com/search?q=%22shutting+down%22+versus+%22turning+off%22+the+computer

"optical mouse light stays on"
://www.google.com/search?num=30&hl=en&lr=&safe=off&q=%22optical+mouse+light+stays+on%22

Hello.

I would like to add a few words to what has already been said/written
on the matter.

Since the original question was "should the computer be _shut_down_ or
turned off?", RAM defragmentation is not really an issue in this case,
because both shut down and power off procedures involve clearing the
contents of RAM so it is really not relevant. In fact, even restarting
your computer would clear the RAM. Qutting to DOS and restarting
Windows from command prompt would clear the RAM just as well.

As to the optical mouse light, you should have noticed that the mouse
is not the only device to stay ON after you shut down the machine. You
might have noticed that keyboard lights flash when you TURN ON the
power switch but haven't yet switched on the machine. This is done to
let you switch the computer on with a keyboard hotkey.

However, you should not really be much concerned about parts of your
computer being ON because there is a bunch of electronic devices in
your home that use the same 'standby' principle. Were you ever aware
that your TV that you shut down with a remote control is never turned
off completely, for obviously there should be a small circuit to sense
the remote signal when you need to turn it back on. Same about your
microwave and your VCR etc etc.

Your PC has a similar circuit called 'standby power source'. It is
used to provide power for devices that could possibly be used to wake
up or turn on your computer, including mouse, keyboard, modem, LAN
(network) card etc.

Hope this clears it up a bit. :-) Good luck with your computer!

After recovering from a bad crash with Windows ME, I have been
shutting it down whenever I am not using it. This seems to be working!
Left on overnight, or for extended periods of inactivity, Windows
changes things, updates configuration files, etc. and (I believe)
gradually destroys itself. Shut it down quickly, each time you finish
and it will hold up better. A quick boot and a quick shutdown seem to
indicate a healthy system.