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[ The PC Guide | System Care Guide | System Care: Protecting Your PC | General System Care Factors | Power Care Factors ]

Leave the System On or Turn it Off? (Thermal Stress vs. Wearout)

One of the endless debates in the computer world, along with such controversies as the use of parity memory or the choice of IDE vs. SCSI, is the question of whether or not, and for how long, a PC should be left running when it is not in use. This section takes a look at this matter and explains the issues so you can decide what is sensible for you and make a decision on your policy for your equipment.

The basic question is: you have a PC on your desk at the office. You use it all day. When you go home for the night, should you turn off the PC or leave it running? This is not a simple question to answer because there are so many different factors involved in the decision in most cases. And the decision also depends on the type of PC: a high-end server is more likely to be left on 24 hours a day than a PC used twice a week at home:

  • Convenience: For many people who run multiple applications at a time, having to reboot the PC every morning is a pain in the rear end. It can take me a good 10 minutes in the morning to boot my machine and get my working environment set up the way I like it. Also, I like to run maintenance tasks during the day while I am at work. I will concede that not turning off the PC because you don't want to restart all your applications may be laziness on my part, but it is a significant reason why many people leave their machines on overnight.
  • Power Consumption: Leaving your PC running when you are not using it wastes electricity. That's a fact, so I won't sugar-coat it. On the other hand, it doesn't waste that much electricity, if you leave the monitor off (which you should be doing anyway). You can also use power management to reduce the amount of electricity used during idle periods.
  • Thermal Stress: After your PC has been off for many hours the components will be at room temperature. When the PC is turned on, the components will heat up, sometimes to much higher temperatures than 70 degrees F, causing them to expand. Then when you turn off the PC they cool down again, and contract. This cycle of heating and cooling causes thermal stress in the components that make up the PC, and is a leading cause of system failure (this is also what normally causes light bulbs to fail, which is why they usually pop when you turn them on, and not out of the blue). Leaving the PC on all the time greatly reduces thermal stress, which can lead to increased life for the system. Strange as it may seem, most components last longer if you leave then running 24 hours a day for years than if you leave them off for 22 hours a day and on for only 2 (but this isn't true of all components.)
  • Wearout: The opposite factor to thermal stress is wearout. While leaving the PC on all the time reduces thermal stress and hence prolongs system life, it also causes components to wear out more quickly. This is more of a factor for some components than others--especially monitors.
  • Cooling: It is important to remember that some office buildings run with automated thermostats that turn off the air conditioning at night; if it's 95 during the day and 80 at night, the PC will be quite warm in the morning when the power comes on. In this case you may be risking the system overheating by leaving it running at night.
  • Risk of Power Interruption: Leaving your PC on for long periods of time exposes it to the potential risk of power spikes and surges, brownouts, blackouts and other problems. If you are using a good-quality UPS then this is not really a factor, although remember that unless your UPS supports power-down signaling to shut down the machine, a one-hour blackout will result in about the same abrupt shut-off of your machine, just a few minutes later than it would without a UPS. If you are not using a UPS, and you are in an area prone to power problems, leaving the machine on all the time may be unwise (you should be using a good power conditioning device if this is the case, anyway).

You need to decide for yourself what decisions you want to make about your PCs. My personal stance on the matter has changed over time based on my computing habits and as I have learned more. I now have a basic policy of turning off the PC if I feel that I will not be using it in the next 24 hours. At work, I leave my PC on overnight during the week, but I turn it off over the weekend or when I am out of the office. At home, I usually leave my PC on all the time; I use it every evening and during the day on weekends, I run backups overnight, and I have automatic maintenance tasks that run during the day on weekdays. Remember that I live in New England; if I lived in South Florida and had no UPS, I might reconsider this policy due to the electrical storm activity, for example.

For me, this makes sense, and I acknowledge the tradeoffs I make in doing this. I greatly reduce the thermal stress on my main system and hard disks, but I increase the chance of wearout of these components. I keep the monitor off for safety and to prevent wearout. I also realize that I am spending some money on electricity to keep the system going all the time but it is worth it to me to do this.

Warning: There is one thing I feel rather strongly about in this matter--monitors should be turned off at night, both to prolong the life of the equipment and for safety reasons as well. This subject is discussed in more detail in the care section on monitors.

Next: Power Management: Pros and Cons

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