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Leave it On? Turn it Off? WHY?!

Tuesday, December 13th, 2011 by | Filed Under: Computer Terms, Hardware & Peripherals

Cheryl from Caldwell Oh. writes:

I have heard that you should shut your monitor off but leave the CPU on, what is the reasoning for this?

Hi, Cheryl.  This is actually a question that has plagued geeks practically since the beginning of computers – and if you ask three geeks, odds are that you’ll get three different answers. Since you asked this geek, here’s my answer…

The idea of turning monitors off when not in use goes back to the days of monochrome CRT’s, PSS (Pre Screen Saver).  These things suffered a malady that has returned to plague plasma TV owners called “burn-in”.  That’s when an image is left on a screen for a long period of time, it literally “burns” into the screen.  Here’s a pic of an old Pac-man video arcade screen that has burned in.

Bear in mind, as you look at this, that the screen is not only off, but also removed from the video game.  The situation is less serious on Plasma TVs, because a plasma screen will eventually “heal” a burn-in when it has had enough varying images displayed on it, whereas old CRT’s wouldn’t.

So back in the old days, when you had a mainframe or something that you had to leave on all the time, the common wisdom was to turn off the CRT’s when not in use to prevent burn-in.  Screen savers eliminated a lot of these problems because they could be set to display a shifting image of some sort.  With the advent of LCD’s, burn-in became largely a thing of the past for computers.

Now the main reason to turn your monitor off when not in use is to extend its life.  Modern LCD life spans are calculated in display hours.  The thing to bear in mind, though, is that the life expectancy of most modern LCD’s is somewhere around 100,000 hours.  How long is that?  Let’s put it this way… if you left your LCD on twenty four hours per day for ten years you would age it about 85,000 hours.  In other words, it’s not a real worry.

The primary reasons to shut off your CPU (tower) are two-fold.

This first is that you may want to shut it down when you’re not using it to save wear and tear on your machine.  Lots of little moving parts and things carrying electricity and stuff that wear out more quickly the more that they’re used.  There’s also the possibility that a power surge or something may hit that damages your machine if it’s on.

The second is that, every time that you run a program, little bits and pieces of that program are left in your RAM.  Enough of these little bits and pieces will eventually cause your machine to slow down. Because of this, I’d recommend that you reboot your machine at least once per day to clear these out.

The main reason to leave your CPU on is that it’s constantly in a “ready” state,so when you go to use it, it’s all ready to go.

One way to fix all of these problems (except for the bits left in your RAM) is to use your machine’s power options to turn your monitor off and put your machine to sleep after a certain amount of time inactive.  Then, when you’re ready to use your machine, all you have to do it click or move the mouse to wake the machine up.

Hope that this helps.

~Randal Schaffer

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8 Responses to “Leave it On? Turn it Off? WHY?!”

  1. Mike says:

    One reason to leave your computer on – especially if it is a work computer on a network: the company IM guys may be pushing updates after hours. We have to leave ours on for that reason.

  2. Dan says:

    you forgot or you are a member of the throw away society. Save energy whether you are paying for it or your boss is.

  3. Premium Member says:

    Excellent answer….also I was not aware that Plasma TVs suffered burn in.

    I’m an old B&W and color picture tube expert. Still trying to catch up.

    I travelled a lot and at the airports they were all burned in, especially in Russia and Poland.

  4. Robert Wurzburg says:

    I use a ‘blank’ screensaver. The monitor display is turned off, while the
    screen is black. Using any other screensaver, shortens the life of the CRT
    turning the pixels on and off while the screensaver makes its way around a
    monitor’s screen. It’s like having the monitor on, just portions of it at
    a time for a short time.

  5. Tim says:

    Randal, I’ve been in the computer world since 1980. I’ve been through all stages of PC monitors from the old monochrome green screens to today’s hi-res LCD models. And I’ve had the same question as you answered here dozens of times a year. Your answer it the most concise, reasonable and up-to-date I’ve seen in “print”. Keep up the good work. One other consideration, of course, is the “green” option. Conserving power is becoming far more of an issue than ever, and for that reason I’m powering off the home CPU tower and display when not in use.

  6. randal says:

    Hi, guys. Thanks for all the great comments. Let’s see if I can address some of them.

    Mike, true enough. I hadn’t thought of that. At my day job, they do all of their updates overnight so that they don’t slow down the network when everyone is using it.

    Dan, I’m not sure what your comment means. I didn’t say or mean that you should turn it off if you’re paying for it, or leave it on if your boss is paying for it. Conserving energy is a great idea, and if you meant that I should have mentioned that, you’re probably right. I should keep my own environmental commitment at the forefront when I write these articles.

    Robert, you’re right about that. When I talked about screensavers, I didn’t mean to imply that they’d extend the life of your monitor beyond preventing burn-in when this was a problem.

    Finally, Tim, thanks for your nice comment. It’s comments like this one that keep me going.


  7. Jadesqr says:

    “LA LA LA LA LA”, way to much information Randal. Now I’m confused. If Cheryl has a CRT she should naturally shut it off when its not in use, but I have always heard let a well running PC run so it will ‘auto-update’ Windows, anti-virus, Norton at those odd times when its not in use. Only exception is electrical storms and schedualled power outages. Obviously, the LCD could be left on for ever. So which do you recommend, really?
    PS: Don’t see Dan in ‘Responses’, did he DIS the article?

  8. Greg Wynn says:

    Fine info but you overlooked one of the elepants in the room. After all these years I have finally switched to a laptop/notebook. Due to my use it will be necessary to sometimes leave it on for extended periods so how will work, i’m not talking 24 hours plus here, indeed I got into laptops to reduce my enery imprint.

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