eli5: Does it matter to a computer how long it’s powered off for? Is one micro-second as good as 5 minutes? If not, why and how long is optimal for it to be powered off for?

Question

That is the question. I almost never turn off the computer, but sometimes flick it off for just a second or two. Is this bad for it? Does it need rest? Thanks!

In: 1752

Answer 1

There are a few factors that play into this:

* Computers contains a lot of capacitors, and capacitors take some time to discharge fully, Power offs shorter than that may cause some charge, and thus data, to be retained. The exact time varies by a number of factors, but typically will be from 1 second to about 1 minute.
* DRAM, the main working memory for computers, will retain data stored in it for a period of time without power. To ensure accuracy, this memory requires frequent refreshes, typically on the order of every 50-100 ms for modern memory, however some data may be retained for 10 seconds or more.
* This is not to be confused with SSDs and other long-term storage, which does not require power to hold data.

These two are the most likely to cause problems, and are why hard restart instructions typically say to power off for a couple minutes. Such instructions will typically say something like “hold the button for 10 seconds then wait 2 minutes and try powering the device on”. The 10 second hold is to trigger the shutdown sequence, then the 2 minutes is to ensure the shutdown completes and all charges and data are reset. As hinted above, different devices require different times for a full reset, and the longest I’ve seen are about 5 minutes, though there is no reason that is a hard limit.

Quicker restarts are useful, however they may not fully solve problems with the machine. Such quick restarts will not cause problems, they just may not fix certain types of issues – in fact, most computer hardware has a reset button that will be a nearly instant power off and back on.

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The final factor, which should not matter much, is that computers have a non-rechargeable CMOS battery to retain some data and maintain the clock. A power off while that battery is drained will typically cause loss of BIOS settings and the clock. The actual BIOS itself will typically survive, but user settings may be reset. These batteries will typically last for years as they have extremely low power draw – typically the battery will rust out before the charge is drained.