Turn computer off?

Posted on 1998-06-13
Last Modified: 2011-10-03
I have heard that it is better to leave your computer on all the time rather than turning it off.  I have also heard that it depends on the amount of use too.  Please help me clarify this a bit.
Question by:Don Juan
1 Comment

Accepted Solution

laercio earned 100 total points
ID: 1019227
Every electronic or electromechanical can be turned on and off only a certain thousand of times. Some detailed technical manuals, such as hard disks, specify the maximum number of start/stop cycles. On the moment a device is turned on, some stressed condition occurs during a fraction of a second. The electrical current flowing from the power supply hava a peak value, to charge the several capacitors distributed along the circuit boards. Millions of microscopic CMOS transistors inside the chips are charged on the same moment, drawing a high current from power supply. A high and unusual current pass along the interior of the chips, and this causes damage after some thousands of cycles. Electrical motors, such that on the hard disk, have a great current so start its spin. A great temprature increase are suffered by all the semiconductors.

All the devices resist this initial state, but its integrity is slowly degenerated along the years. As you can see, a light bulb is never burned when it is already on, but always on the moment you switch it on. That high current and temperature increase on a short moment is very difficult to support.

When a computer is turned on and off several times along a day, its devices suffer a greater number of electrical and thermal stresses along its life. The greater the number of start/stop cycles, the longer the components will work.

Supose a component with a useful life of 30.000 start/stop cycled. This not means that after the 29.999th cycle, the next will be the last. These number are statistical, and the actual number can be greater o smaller. The probability of the actual number be on the range [29.000, 31.000] is far greater that the probability of the number be on the ranges [28.000, 29.000] and [31.000, 32.000] together. This is usually a kind of gaussian distribution.

Suppose a component with resists a small number of start/stop cycles, like 3.000. This is about 9 years. I thing from here to 9 years your computer will be completely obsolete.

I do not recommend to let the computer turned on 24 hours a day, because other problems can occur. O loss of power can damage data, a storm can send electrical perturbations along the phone line, and even on the electrical network, the electrolytic capacitors that have a short useful life (the correct is to use tantalum capacitors, but manufacturers of second line boards use the cheap electrolitical capacitors) will be damage after one or two years, and so on.

To avoid both problems, I recommend to turn on an off the computer only one or two times a day. Turn it on in the morning and let it on until the hour to go home. Use the lunch time for backup. Use a screen saver with password to avoid some one use your computer during lunch. If you want, let it turned off during lunch time, it will be only 2 start/stop cycles each day. The life of your computer will be very long.


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