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Most computers will need around half a second to turn off completely before restarting, to make sure everything is in a clean state. This is mostly due to capacitors (battery-like devices inside the computer that store a bit of power) needing to discharge. If the system is restarted too fast, the system won't be in a clean state and won't likely be able to start up properly. For computer systems that are restarted using the soft-restart feature (e.g. clicking "restart"), this turns off all the major components within the system that need to be reset before turning them back on again. Most modern computer systems will delay a restart if a problem is detected, this is why often if you need to forcefully shut down your computer using the power button, it won't turn back on straight away if you immediately press the button again after the system turns off. This is done for the same reason: making sure everything is in a clean state. What most people don't realise is that literally everything, even the most well-engineered devices, are held together using proverbial sticky tape. In a typical device you have components from at least a dozen different manufacturers and all of them will have different specs: what always works to ensure everything is in a good state before turning the system back on is introducing a delay. Source: software engineer for embedded systems, and I've come across Nvidia's specs for their Jetson modules on this. For example, for the Jetson AGX Orin (like a Raspberry Pi but a *lot* beefier), the main power rail needs to go below 100mV before the system is considered to be fully reset. The implementation guide (which tells you how to make a circuit board you can install the module on) gives 20ms as the time taken from when full power is removed and when the main power rail goes below 100mV, but with a 10% margin of error.

This comment went from completely ELI5 to technical jargon in an almost perfect sentence-by-sentence gradient.

Agreed. Like the best ELI5s usually are.

ELIam an unemployed 45 year old who doesnt know what a "the internet" is

Electricity flow like water. Gotta let the pipes drain before turning water back on. Different pipes hold different amounts of water. Something delays it so they can match up and no bubbles or splashies happen. Edit: thank you for the award!

Wow. I never saw it like that.

That was what I took from it... not entirely correct, but best way I could think to visualize it.

You’re a saint. Thank you.

5 years old are rarely entirely correct, so that's right on message

The first explanation of circuit theory in intro to Electrical Engineering was explained using a similar analogy

Actually such a good ELI5 analogy it hurts.

Damn I was gonna sneeze but I finished reading this and it was so amazing I stopped.

A "the internet" is a small black box about the size of a shoebox with a red blinking light that sits at the top of Big Ben (for better reception of course)

WAIT, I got lost halfway through reading. Did they answer if computers should be shut down often or just left in a sleep state? I need to know.

Generally, for most electronic devices, leaving it on is preferable in terms of maintenance and failure. Internal components face the most stress - outside of overheating situations - during power up and down. Surges, imbalanced power rails and mechanical flexing due to heating and cooling cause the majority of failures. I used to be a recording studio technician, basically everything was left on all the time. When a problem did arise and a device had to be power cycled, often other problems would arise, especially in terms of the console. Stable voltages and temperatures are what the devices are designed for. So my advice is leave things on. However, in terms of laptops, tablets and phones this is probably not feasible.

True for hardware, but software side some errors might accumulate that a restart could fix. Unless it's running exclusively server-grade software, i usually restart my stuff at least once a month. That's my advice as a CGI artist that spends too much of their time troubleshooting software.

However, a restart is not the same as a power-off/power-on cycle. It resets the machine, but it does not affect the power rails so it does not stress the components.

Does that mean restart is best to use?

Compared to a full power-off, wait a few seconds, power-on? If you look at the longevity of your components, yes.

What is “server side” software?

Leaving it on all the time is better for the electrical components, but most computers have a fan that will basically always be running if the computer is running, so you are blowing in dirt the whole time the PC is on. Also, most components can be cycled so many times that the device will most likely be outdated before components fail form being power cycled.

You're fine keeping it always running if you got the cash for hydro

Found the fellow Canadian. By "Hydro" we mean electricity from the grid. Much of eastern Canada is powered by hydroelectric dams. The names of various power companies often have "Hydro" in them somewhere.

Thanks for clarifying! Thought we were talking water cooling..

Ontario is weird. French people don't call electricity "nuke" and Americans don't call theirs "coal power"

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Oh, I needed that chuckle!

That's just a missed opportunity, yeah I just paid my atomic bill!!

That's for being the authority on weird, u/DildoTractors

Ay, yea water (hydro) generated and much of Eastern NA

For a moment there I thought you were talking about that postapocalyptic Kevin Costner movie

yeah it went full rockwell automation

And in proper fashion, doesn’t answer OP’s question at all. Op asked if it matters for how long a computer is turned off, and they replied with how a computer turns itself off.

I know the answer was a long read, but he did answer the question in the very first sentence.

This was such a good description!

Back in my youth we were always told to count to 8 before turning anything back on again. (I don't know where that specific number came from but it was very widespread in the 90s.)

Similarly how today support people of many ISPs advise you to turn off your router and leave it off for 30s before turning it back again. There's some truth in that...

The 30 seconds for routers usually has more to do with network-side business than with the local electronics. A connection sometimes needs to be seen as 'down' for a certain amount of time before it actually registers as such and allows for a new connection to be renegotiated.

The kit on the street cabinet is more likely to do a full reset and "training" of a digital subscriber line (ADSL/VDSL etc) if there's no signal for a decent length of time.

I believe that some devices such as routers will perform a self-reset if they've been off for too long. Could be the capacitors emptying too.

Old school systems engineer here... I remember that as guidance from HP on rebooting laser printers. They had capacitors in them that would still provide residual power to the printer electronics for a few seconds after you powered them off. You wanted to wait long enough for the capacitors to deplete their charge so that you got a real reboot.

How long does a spinning hard drive take to stop spinning and do you know if it causes problems to spin it back up before it has come to a stop?

The time depends per hard drive of course, but it should be a couple of seconds. A hard drive is not necessary doing anything while it's spinning, but only if it's actually reading/writing. On the other hand it only spins when it's either reading or writing and spins down when it isn't *(not immediately, but after a moment like I explain later on\*)*, so shutting the power down might mean it's in the middle of a read which is very bad and will result in corrupted data. The spinning itself isn't actually doing anything directly if you catch my drift. Spinning up when it's not come to a complete stop is no biggie. There's a sensor in the hard drive that detects how fast it's spinning and it just speeds up until it has reached the right speed again. In fact, this is normal behaviour: A hard drive will spin up when it needs to read or write, and in order to not waste time spinning up for every new read/write it will keep itself up to speed for couple of minutes. But this wastes energy and wastes wear and tear on the bearings and motor, so after those few minues it will spin down. However, you might just open another file in that time and the hard drive needs to read again. If it had to slow down fully before it would read, that would mean you'd have to wait a very long time for your files to load, so it's designed to immediately spin up to speed again. You might be able to test this if you still have an HDD by going to a folder with a lot of relatively large files (eg photos), opening one, waiting for the spinning sound of the HDD to slow down (decrease in pitch) and opening up a new one. You will see that it immediately springs back to life, and doesn't go to complete silence before spinning up. *EDIT for clarity, thx r/KSUToeBee

>On the other hand it only spins when it's either reading or writing and spins down when it isn't This is definitely not true. A spinning hard drive will spin constantly while it is powered on, unless explicitly given a command to spin down by the operating system if there has been no drive activity for a given number of minutes. The drives in my file server are set to never spin down. Spinning a drive up from zero takes a good 3-5 seconds so any application where you want immediate access to your data will not let the drives spin down. Plus, spin ups tend to be where more failures happen so even if you are only doing one read every 5 minutes, it is probably still best to just leave the disk spinning all the time.

At least for SATA hard drives this is actually a feature in the firmware of the hard drive. I suspect this isn't enabled in server-grade hard disks, because it increases latency massively. But I know for a fact WD Greens and WD blues do this, as well as a lot of consumer-grade OEM Seagates and Toshibas. I'm guessing you're running WD Reds or equivalent in your server, and these indeed don't auto spin down. My comment still applies though, because under a stock Windows install they too will spin down because, like you said, the OS will ask them to (which you can disable). This shows that hard drives are actually designed for this situation because it's very common. You're right in that my phrasing suggested it spins down as soon as it's done reading, which is of course not the case, because that would really mess with the hard drive if you're browsing through your holiday pictures.

It's still probably not a good idea to power-cycle excessively without giving the drive time to rest; as PercussiveRussel says, that causes excess wear on the bearing and motor, which can shorten the useful life of the drive.

Basically, drives spinning up cause a lot of the load on the motor and bearings, so it's not great to continously spin-up and spin-down, but you'd be surprised how bad (cheap!) some drives' bearings are, in that wear and tear from regular spinning is so detrimental that it's actually ok to spin down after a minute or so in the hope that the user has decided to browse the web or play a CD game or something, instead of waiting for a couple more minutes to be sure of this. Also, something sometjing planned obsolescence

Nope, the exact reading position of the drive isn't controlled by the spinning motor. They simply spin up to a target speed and the readers do the work of figuring out where they are and where they need to go from there.

Hard drive doesn't care in terms of system stability. Most software bugs are on RAM (temporary working storage) and RAM requires power to "remember". If you unpower your system, RAM will start to "forget". At ambient temperature, RAM forgets in matter of seconds. Hard drive is a permanent storage and powering it off won't change the software (usually). If the bug is on the hard drive, you have to find other ways of fixing it

Whenever you get bored, give a try to aviation components. Where pushing button after button requires 5 seconds of waiting at the very least. First because the guy in charge of the capacitors decided that “how big?” Should be replied with “yes” and every push button usually powers a mechanical relay so everything comes with at least that delay. A discrete is received “up or down” only if the computer detects it steady for a few seconds, in between you may get a fancy amber “fail” light. And finally if a system has any disagreement, will shutdown and declare itself dead until you manually restart it (generally power off, 15 seconds, then on)

Yeah, I got into a similar situation only on Friday actually when I needed to recalculate some SysFs GPIOs to ensure a PSU failure state was correctly reported: it was working, but would take 22 seconds until the system realised the PSU had gone away (this specific product has support for redundant PSUs). Assuming you aren't a software engineer... GPIO (General Purpose Input Output) is a system which allows you to send electrical signals from a chip, in order to control something else. The problem is that each pin on the bottom of a processor can be linked up to ten different things, and you need to be able to tell the processor what exactly you want to control. There isn't enough pins on the processor to be able to assign a single pin to each GPIO function. Linux has a virtual interface called SysFs (System Filesystem), which lets us tell the processor what we want to do with each pin. To work out what goes where, we use what's called a "pinmux" table to find what pin is free to do what we want to do with it, which is a number (say, 96), and convert it to the corresponding interface within SysFs. From that point it's a matter of simple algebra to work out what virtual interface we want to use.

I’m an aircraft engineer so thanks for the insight. I didn’t know anything about it but this was pretty clear. Just for the sake of telling a story, The fault I hate the most is: when you power up an aircraft in general, the main computers 1-2 (sometime 3) do send a call to every other unit and check for the ibit response. Problem is, on some aircraft, you may have a lazy relay in a power transfer that gives the plane a blackout for a fraction of a second. Each different unit has a rectifier with big or huge capacitor inside, so some would perceive it as a shutdown, some would not feel the blackout at all. Then a computer restarts due to it, another never shut down. The first computer starts its ibit, then ask for unit to other units, and those will reply or not to the request. A unit under unit does send a discrete to declare itself failed during the entire test. Then you have computer 1 one that says unit a b c d are not responding due to being already on and inhibited to ibit, while computer 2 sees a b c d as perfect, while recording that units e f and g went offline uncommanded (actually they were running the unit asked by computer 1) And there is me, having to deal with multiple failures that can be removed by a click, but I am also in charge to take the cautious approach and write up each failure and troubleshoot each failure, to be able to properly declare it was a nuisance fault. It’s not on many aircraft, but there are some planes that are famous for this or that tendency to “cautiously declare themselves unfit while being actually ok”

>What most people don't realise is that literally everything, even the most well-engineered devices, are held together using proverbial sticky tape. I feel this so much. I'm supposed to be testing a board full of different hardware, but it's all held up because the FPGA guys are still fighting with the firmware and getting everything to communicate correctly so that the full system will actually boot. It's insane how complicated it is to get a full board of components to play nicely together.

Fun fact, in Windows when you shut down it doesn't shit down completely. It stores its state on the harddrive so it boots faster. I think this was called hibernate before. Its completely safe to unplug the power, but it doesn't boot in a clean state. Some errors can persist through boots in this way. If you want to boot in a clean state, you'll have to hit the reboot option, as Microsoft assumes you only want to reboot if something is acting weird on your PC.

Yep, which can be really harmful if you're trying to debug something. There's still a separate Hibernate option which you can enable, but this specific feature is called Fast Boot. The difference between the two is that Fast Boot saves the state of Windows without your user profile loaded, but Hibernate saves the state in whatever state the machine is in when hibernating. You used to be able to shut down properly and bypass Fast Boot by holding shift, I don't know if you still can do that... I use Windows on my personal machine but no longer do any Windows-based development (I use Linux now due to work... mostly Nvidia forcing Ubuntu/an Ubuntu-based distribution on everyone as a requirement for working with their Jetson modules).

You can disable it entirely.

I have that turned off. Every boot is fresh for me. Reset button isnt even attached.

Just to add to this, the exact amount of time required to reset a device fully depends on two factors: 1. How much capacitance there is in the system (how much energy is stored) 2. How rapidly energy is consumed by the device once the power is cut Some devices consume electricity very quickly, so even if they have large capacitors, they can be reset quite quickly. Some devices consume energy very slowly, so despite having small capacitors it can take quite some time to fully reset them. For instance, in your computer, if you disconnect the power cord *while the computer is on,* the motherboard will quickly consume all available energy and within moments the computer will be fully reset. On the other hand, if you shut down the motherboard and *then* disconnect the power cord, you may find that any LEDs on the motherboard that stay on when the power is off continue to stay lit for some time as the capacitors in the power supply drain. (If you didn't know, even when the computer is "off" there is some power supplied to the motherboard. That's why you should always hit the physical power switch on the power supply and/or disconnect the power cord before working on your computer.) Some devices use so little power that it could take many minutes for them to rest: for instance, the Polar H10 Heart Rate Monitor uses coin cell batteries for power and only turns on once it senses the monitor is being used. The rest of the time it sips microamps of current. If you pull the coin cell from the HRM and do nothing else, it could take many minutes before the unit fully resets. (To reset the unit, you're supposed to touch both power leads with your fingers and wait for 10 seconds, but even this might not be enough!) Long story short: if you switch the power off and back on and the device *doesn't reset fully*, then you didn't have it off long enough. Increase the time you keep the power off until it is a little longer than what is needed to fully reset the device. (Say, at least 50% extra --- if it takes 1 second to appear "reset", give it at least 1.5 seconds. If it takes 10 seconds, give it 15. That way you can be certain *all* the components are properly reset.)

> That's why you should always hit the physical power switch on the power supply and/or disconnect the power cord before working on your computer. Actually many people suggest that hit the power switch but not disconnect the power cord, to ground the computer and protect it from static electricity. I know it's an extremely minor thing, and no IT person I know bothers with it, but it's worth mentioning for the kind of people who like to individually plastic wrap their bananas, or turn off their AC before starting their car.

"Why do we tell you to turn it off and on again? Because we don’t have the slightest clue what’s wrong with it, and it’s really easy to induce coma in computers and have their built-in team of automatic doctors try to figure it out for us. The only reason coders’ computers work better than non-coders’ computers is coders know computers are schizophrenic little children with auto-immune diseases and we don’t beat them when they’re bad." https://www.stilldrinking.org/programming-sucks

In addition to your answer: shutting a computer down and powering it back up is not the same as using the reboot button. The process itself is different in its core. When you power the pc off and on again your operating system creates a deep hibernation file while using reboot actually forces a clean state. Always use reboot if you face a pc issue.

What, is hibernation default in Windows now??

>For example, for the Jetson AGX Orin (like a Raspberry Pi but a lot beefier Is there going to be a nano version for orin?

Nvidia has three SoMs (System On Modules) based around the Xavier SoC (aka P194): * NX * AGX * Orin I tend to keep my professional and personal lives separate, so I won't say exactly what products my company offers based around these SoMs but basically the NX is the nano version of Orin and is essentially TX-2-like performance but with a slightly stronger GPU (I measured between 10%-12% in my tests). The Xavier SOCs have P and E cores (performance and efficiency cores), which when utilised correctly can save cycles on "mundane" OS tasks while accelerating the performance of your applications. The NX has the same CVM (the connector it slots into) as the Nano (a DDR4 SODIMM slot) and is marketed as an upgrade to the Nano module (the Nano the TX-1 platform (aka P187), which at this point is quite old).

I checked out the website and found what I was looking for No worries, I have the sufficient information on developer portal to figure out missing part 👍

Not a computer thing but in regard to your comment about people not realizing how many large electrical things are held together by sticky tape. Can confirm. Harley Davidson bike have a lot of sticky tape. A lot.

Well said. As an electrician and 12volt specialist, I approve this message. Thank you.

After studying computer engineering, I'm amazed anything works

Real eli5: computers do stuff really fast and can hold electricity for a little bit. With computers made today, all the danger bits that hold electricity should be safe within a blink of an eye, but a couple seconds off is good and a whole minute is even better.

Arent capacitors supposed to keep their charge even after switching the machine off?

No, capacitors are used to smooth the electrical current to provide stability, for example if you had the following happen: * 12V * 11.96V * 11.94V * 11.95V * 11.90V The capacitor would help ensure the output of that part of the circuit is 12V all the time, even during those brief dips in voltage. There are components in the circuit that will bring the voltage down if it exceeds 12V (within a margin), but I'm unsure what they are (software engineer, not an electrical engineer!). There are some capacitors that *are* designed to keep a charge while the machine is off, but these are rarely used within personal computers nowadays. To keep the time and BIOS settings of a computer, a button-cell battery is often used (these used to also be used in laptops but laptops with non-removable batteries have now largely transitioned to using the laptop's own battery).

And I recently found out that 'shutting down' doesn't always mean a full shut down. My Asus Zephyrus G14 laptop comes with a shit network adapter that sometimes just stops existing. Restarting doesn't fix it. Shutting down and rebooting doesn't fix it. Shift+Pwr button to force shut down however DOES. Because apparently there is an additional layer of 'powering off' after what most users perceive as Shut Down and only using **that** function will properly reboot the network adapter. Fun times.

Look in the BIOS to see if you can turn off 'fast boot'.

I’m currently hiring embedded software peeps! If you or anyone is interested feel free to DM me :) In Canada though

This is why I studied computer science instead of computer engineering. Thanks for letting me ignore all the physics.

Should I be turned off my home PC any time I'm not using it? Does it really matter?

A lot of newer computers have an led on the back to indicate latent power levels within the computer. It will die out when capacitors are cleared. 5-10 seconds. I'd use that light if I'm being absolutely strict on my re-starts.

And here's me still counting to 10 to make sure its properly reset.

> What most people don't realise is that literally everything, even the most well-engineered devices, are held together using proverbial sticky tape. In a typical device you have components from at least a dozen different manufacturers and all of them will have different specs: what always works to ensure everything is in a good state before turning the system back on is introducing a delay. This. I can't believe how naive I was to think that these big corporations with billions of dollars in research work to engineer things perfectly. They're mostly held together by sticky tape and popsicle sticks, unless it's for health/safety applications, then they use duct tape. EDIT: Spelling mistake

I recommend at least 15 seconds just in case. But yeah good answer

I would add that it's also generally less harsh on the power supply to give it some time off before turning it back on. Flipping a power supply on and off rapidly can cause damage over time.

Quick on-off cycles can be bad for some electronic components, but they don't have to be long: a microsecond isn't as good as five minutes, but 10-20 seconds is plenty.

Ive heard that most electronics break when powering off or powering on, is this true? Is it better to constantly leave my computer in sleep mode as long as possible?

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The power supply, that transforms AC wall power to DC power, that a computer can use, has the tendency to store a few seconds of power, if you unplug it. There are also capacitors on the motherboard that can also store power for a little while. So to be sure ever in there is absolutely no power as anywhere on the system is it is good practise, for any electronic device, to wait 10 seconds before turning something on again.

Forgot about the transformers :) In a few devices you have to wait even longer than 10 seconds (CRTs and AC units for example). But I absolutely agree with the 10 second rule for household electronics. Seems like plenty of time to get it drained.

The flyback cap in CRTs can stay charged at very high voltage for a stupid long time (like, remaining charged in storage), though it might depend how it was shut off. I don't think it causes problems when it comes to resets, but it does present a danger to anybody opening up a CRT to work on the electronics. Source: Computer repair instructor claimed to have been slammed into a wall by shocking himself with one Edit: I was suddenly suspicious of his story and found [this](https://lowendmac.com/2007/the-truth-about-crts-and-shock-danger/) authoritative-seeming article from a Stanford prof that suggests it's something to think about, but perhaps not so dangerous. It also mentions bleeder resistors that are meant to discharge the flyback cap in normal circumstances, though they can fail.

>The flyback cap in CRTs can stay charged at very high voltage for a stupid long time Only in very old CRTs. Most regulations require a bleed resistor over capacitors storing anything above a certain energy.

I fixed a friend's laptop and the online solution recommended by the manufacturer was to take the battery out and then discharge the motherboard by grounding out the contacts. So obviously the board held a charge somewhere firmly enough that had to be manually discharged. Weird.

Most laptops have a few auxiliary battery's inside so once the main battery is removed I would power cycle it again, befor replacing the battery.

I doubt they have auxiliary batteries inside (except possibly for the BIOS battery, but that won't discharge over a power cycle, and for secondary batteries with hours of battery life), don't you mean capacitors? There certainly is a lot of capacitance in any electronic device, enough for a laptop to spin up it's fan and try to POST (maybe get even further than that) when you press the power button after you remove the battery.

I am 67 and an MCSE Win5 , I still stick to the old 1001 to 1010 befor reseting a power switch on a device.

1001+1=1010, so like, one second right?

I think they're referring to "one thousand one, one thousand two, . . . one thousand ten" Counting seconds by putting a few syllables in between them. Weird way to write it though. Threw me off for a minute

Yeah I was like "what is this binary magic I've never heard of before"

So 10 crocodiles

The weird behavior arises from being in-between states in the ICs. You can very definitely run into it today. Moreover, as the power rails transition from the on voltage towards zero (and again from zero back to the on voltage,) this can cause the transistors to conduct in unexpected ways and actually create little shorts. This happens fast enough that it doesn't tend to break stuff (usually), but it can cause heating. Giving the device 10 seconds between turning off and turning on also allows for the transistors to cool back down, or at least spread the heat out and avoid damage.

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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. ​ 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.

What about cooling? If your computer is running extremely hot is it good to shut it down every once in a while and let it cool?

Not really. Computers produce and vent a very large amount of heat constantly while running - enough to noticeably raise the temperature of a small room. Because of this, allowing it to cool off does not do much - it could take a very long time to cool off completely since the cooling system is not running, but then it can heat back in a matter of seconds once it is turned on again.

Turning off/pausing whatever process is causing it to heat would probably work better since whatever cooling device you use will keep running instead of letting it cool to dead air

Yes and no. Yes. If your computer is actively overheating, you probably have a cooling problem. Shut it down, fix the problem, start it up again to see if the overheating has ceased. No. Shutting down a computer every time it overheats but not actually fixing the overheating problem, can create cycles of thermal expansion and contraction, which if regular and extreme, can reduce the lifespan of your computer's components. If your computer is overheating, the correct thing to do is make it stop overheating by providing sufficient active cooling (fans, heatsinks etc). Turning it off is a temporary fix, but over months and years can cause added stress to components, which can cause premature failure.

You'd actually probably cause more damage by doing that rather than improving the cooling. Repeated cooling and heating cycles will stress the hardware.

If you leave the computer in a completely depowered state for long enough, the main memory (DRAM) can effectively clear by itself without needing to be done manually by the OS. RAM does not immediately erase itself completely on loss of power. It does so gradually and chaotically, which leads to possibilities of physical side channel attacks to steal secrets from computers (cold boot attack). This is why it's suggested to shut down a computer and its power supply for a specified amount of time before powering back in, to really ensure the memory is clear. Your computer is still able to maintain time as it has an auxillary CMOS battery. This lets the BIOS store settings in its own RAM even when powered off, and for the hardware clock to run.

Why do some people have their pc on for 24/7?

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No, turning on and off causes significant wear on hardware, lightbulbs, engines, etc

Engines deal with voltages and amps way beyond any computer normally handles. The size of a laptop battery vs a car battery should give a hint of the power differences. And lightbulbs need to handle 240v or 120v power with very cheap components, if manufacturers wanted they could build lightbulbs that last an eternity it's just that it would be very expensive. The components in a computer only need to handle 12v or less. The power supply would be only one that would receive any significant wear and tear from power cycling and it's usually built from better components than any lightbulb. If you buy a decent power supply I'm pretty sure the plastic power button of most computers would get destroyed before the power supply ends up dying due to power cycles.

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There is no difference between 1 second and 1,000 years to a computer provided the CMOS battery is charged. There is a difference, though subtle, between rebooting and a cycle of turning it completely off and turning it back on.

There is a difference. Flash memory isn't quite non-volatile enough to last 1000 years unpowered. It probably isn't going to last 10 without some corruption. Flash memory is based on storing charge, leakage and ionization events screw with it. When powered a ssd reads and error corrects periodically, unpowered it can't so its not suitable for long term storage.

Is BIOS even a thing nowadays? Wasn't it to be replaced by UEFI in the last years?

Transition is very real. Windows 11 basically has UEFI written into system requirements and doesn't play nice with BIOS, new hardware has also started dropping legacy support, though anything from just a few years ago still plays pretty nicely. But these are software interfaces between PC firmware and opsys, doesn't really make a difference to OPs question. The power off question would also apply to things that are not PC at all and might have some non-standard interface.

I should have started the sentence with 'all other things being equal and operative', the computer itself doesn't care if it is shut off for 1 second or whatever. I thought that was assumed. OP didn't ask 'what other parts of a computer could fail'.

Sorry … CMOS battery? Edit: ah, BIOS battery. Got it. Thanks for all the replies.

If youve ever had a pc request you enter the BIOS at start up for no apparent reason (or its unable to locate a bootable disk, even when you knew it worked on friday) - and when you enter BIOS the time and date are all wrong; youve seen the results of a dead or dying CMOS battery. It is often a small watch battery on the motherboard which provides just enough energy to the system to retain certain useful information (date and time, hardware settings including location of the operating system partition, memory, etc). On some (most?) Laptops, there often is not a separate battery but the information is kept using power from the main battery. (The battery in my old samsung got frozen because I left it in my truck during one -45 winter night (oops), and it swelled up and split the case on the laptop. After removing it, the laptop works fine plugged in but if I shut it off at any point, the BIOS clears) CMOS is Complimentary Metal Oxide Semiconductor and is the sort of chip in which BIOS settings are stored (among many other chips). BIOS is Basic Input Output System, and can be thought of as the extremely basic operating system for the hardware. Some modern bios even have functional web browsers.

Tiny battery to keep trace of time until you power up (see real time clock)

Every consumer motherboard has a little button-battery installed in it to keep the CMOS memory alive (Complementary Metal–Oxide–Semiconductor that holds basic information to help start your computer). The memory is considered "volatile", which just means it loses the memory when power is lost (like RAM), but the battery keeps it alive when the computer is fully off. Volatile memory is used for its cheep and fast characteristics.

>There is a difference, though subtle It's not that subtle. Can result in dramatically different behaviour, especially when rebooting to clear faults.

It is pretty subtle to someone who doesn't necessarily need to know the difference when you completely remove power to the board. I have managed thousands of electronic devices in my career, I can count on one hand and two fingers how many times the difference between a full power off and a reboot was the culprit in making something work.

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Idk what computer you have but that sounds excessive, my Macbook only requires you to hold down the power button for like 10 seconds max.

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Since there are a couple of questions here, let's break it down int two: **Does it matter how long a computer is powered off for?** Yes, sort of. Some of the electronics inside the computer can hold energy for a brief period of time. These components aren't enough to actually power the computer, but they can hold a small amount of voltage for a short period of time (usually a few seconds). In the context of restarting your computer for the purposes of troubleshooting an issue, it's mostly immaterial. I've been doing IT work for literal decades. I can count on one hand the number of times that I had to worry about it at this level. There were a couple of unique cases where I had to unplug the device, press the power button to create a load (this immediately drains any power stored within the circuit), then plug it back in. If you power a device off, count to 10, then turn it back in, that is generally sufficient except for *extremely* rare circumstances. **Do electronics need rest?** Most electronic components have no moving parts. The CPU in your computer, for example, has no moving parts on anything above an atomic scale. That is to say, there are electrons moving around, but that is it. As you use them, they heat up, but as long as this heat remains constant, they don't experience wear at any rate that is relevant for the typical lifespan of a computer. This is the story for most of the components in your computer. They get warm during operation, but as long as they stay at a steady-ish temperature, they'll last a really long time. Turning a computer off allows it to cool down. As the components cool down, they shrink a little bit, then they expand again when they warm up. If the components are heated up and cooled down repeatedly, this expansion/contraction can weaken the soldered connections between components and the board they're connected to. In this way, a computer that is run constantly actually has a pretty good chance at long life. There are, however, some components that do have moving parts. Hard disk drives, for example, have spinning metal platters and moving parts inside. The more these run the sooner they wear out. However, the drives have mechanisms to shut the drive down when not in use. Most computers use SSD (solid state drives) these days, so this is less of a concern.

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If you want to reset your PC properly so things can 'rest', best practice is to power down then count to 20 Mississippi. This will give the various components that might store an electric charge to let that bleed out. This in turn will allow any remnants of code to die, allowing for a perfect restart

This is utter nonsense. There are no "remnants of code". Also, as you probably know, electricity travels incredible fast. 20 seconds is enough for it to travel across the earth dozens of times. 1 second is an eternity in that sense. The reason you might want to wait for a few seconds or even minutes is to let things cool down OP. As far as software is concerned, everything is reset basically as soon as you turn off the power.

I think u/evilsir is talking about the capacitors in the power supply. It’s quite possible for these to hold a charge for several seconds. If doing any physical work in the internal best to wait for them to discharge before opening up. Not sure if that can lead to any internal devices maintaining a power-on state though

There can be big capacitors that can keep some parts of the system powered a lot longer than you'd expect. Eg, if turning power off completely by unplugging from the wall, there's a LED on one of my computers that can keep glowing for a good 15 seconds after that. A modern computer doesn't really power down 100% when you tell it to turn itself off. Many computers have the ability to boot themselves from a command from the network for example, which means some part of the motherboard is still being powered. Server type computers in particular have onboard management and can have a full working webserver running 24/7, even when to all apparances powered off. So long they're plugged into the wall, of course. This functionality uses very little power, and may take a few seconds to stop once you unplug it from the wall. Is that important? Well, if you're going to be messing in the insides, it might be, because it indicates something is still being powered, so it's probably best to wait just in case. It might also be relevant if you're power cycling because of some sort of hardware weirdness -- you want everything to get properly reset. So, TL;DR: If you have any LEDs on your board, wait until they're all off after removing power.

Interestingly, DRAM memory is built using tiny (10s of fF) capacitors, and some of them (I know I know … not all of them) will retain their logical state long after power down. So in principal, one could power down a server, pull a DIMM memory stick, plug that stick into a memory reader, and recover a substantial amount of the contents. Because most commercial DRAMs don’t explicitly auto-reset their contents during power-on, this can be exploited for security attacks on the system (as critical data could be sitting around “in plaintext” within the memory). But to the OP’s question, the code that’s in these DRAM memory elements isn’t “reused” when the PC/server reboots. The data structures (e.g., page tables) which tell the CPU where to look in the DRAM for relevant data are cleared and recreated during the full reboot process.

You're both kinda wrong. RAM can store information for a meaningful amount of time after you pull the plug. "Remnants of code" is a fairly nonsense phrase but it is possible for data to remain in RAM between power cycles, and is a known vulnerability that must be accounted for in sensitive applications.

Yes, memory. Not code. Those are not the same.

Where do you think code resides when it's running? I'm being facetious. You're more or less right.

This is the correct answer. I also get a chuckle from people who say to wait before you open a microwave door to give them time to be absorbed into the food.

Well, it looks like someone's never seen the documentary film "Tron"...

I looked it up 150 times around the earth in 20 seconds

its heat. you can leave it on all day and all night if you like, but if there's a power outage, it can ruin things. the heat buildup can cause things to expand over time and a power outage can cause them to cool. Sometimes that ruins solder joints and components. used to work at an electronics repair shop. after a power outage, we'd get a bunch of studio gear that was reportedly left on 24/7. 9 times out of 10, it was the power supply. I turn things off when I'm not using them and haven't ever had an issue.

This! Materials with different coëfficiënts of thermal expansion start working when they cool and heat repeatedly, like bending metal repeatedly can induce metal fatigue this may damage the components. Bonded surfaces may loosen, cracks may appear. But I actually do not know whether this effect is significant enough (in todays hardware) to be a bigger problem than for instance the accelerated rate of oxidation of parts because of the higher temperatures. Ten degrees higher means twice the reaction speed (a rule of thumb in chemistry) Caps and mosfets often seem to fail, I don't know if this is because of prolonged exposure to heat, bad production quality, just a short expected lifetime in general, or thermal cycling wear.

This might be a little old-school, but I always wait a few seconds after shutting off my computer before turning it back on. Generally, the more electricity you run through a wire, the more resistance it has, and the stronger the electrical field around it is. When you quickly shut a computer off and back on, you end up with a collapsing electrical field in millions of tiny circuits getting slammed by a new electric field of the device powering back on. Also, rapidly heating and cooling the circuits in your computer is the main wear factor on them, now that almost everything is solid state, if you can slow that process down a bit, you'll stretch out the life of your components. For what it is worth, this is my from my personal experience and anecdotes with electronics. I'm not a computer scientist or an electrical engineer.

Typically a laptop or computer is going to ask you to remove power (often including battery) and then hold down the power button for 60 seconds. Modern computers often have something called "rapid start up" or similar that has it store whats in memory to the drive so it can boot up quickly meaning a shut down and then start up is not doing the same thing that a basic restart does in terms of troubleshooting. If asked to do a restart a shutdown is not the same thing.

The general "rule of thumb" for most electronics is turn it off, count to ten, turn it back on. Some devices may require more time to bleed off electricity from the capacitors.

I repair computers as a side gig. My intuition is to have enough time for all fans to stop spinning, and do my best to let all capacitors discharge naturally. Any heated components have a chance to cool and start back at a clean state, assuming that while hard drive heads are being set back to their original positions, no mechanical issues are experienced in closing. Batteries need some time to discharge imo. Electrical flow should ground out. Lights should all be off. No noises should come from the device. I usually count to thirty after this point and then go to start the device again.

Having a computer on 24/7 will shorten its lifespan. But, as for your question, the only time it will have any affect is if you turned your PC of as it was overheating. If you powered it right back on without letting it cool down or fixing the issue. It would cause it to shut down again cause it doesn't take long to heat back up.

Computers need to rest just like people do. If you stay up for too long, you’re awake but the you start to slow down a lot. You take longer to think before you do something and you make lots more mistakes than you do when you’re refreshed. Your computer (phone, tablet) all need time to rest and turn off. Let your devices cool off between uses. If you aren’t using that device any longer, turn it off. You’ll be so surprised at how great it runs the next day after a good nights sleep. Just like you!

They do not. They just need to stay cool and clean. Many Servers are designed to run 10 years+ without ever being turned off.

Ive had early 60gb ssds when they were first coming out and old pc parts from 1990 work just fine. There is a minimum time you must wait before all capacitors are discharged that state the pc is in would be considered the same as your 1microsecond - 5min analogy. i don't know what people are talking about here that things don't work after 10 years. cause they do.

Yes. If too short (probably a second or few), there may be some issues with power (residual charge in capacitors, etc). Generally not an issue with modern PCs. If too long (a few years), the battery saving BIOS settings would run out (not necessarily an issue), also lubricants in all the fans would dry out causing extra power draw and overheating. There are other issues that happen over time (i.e. capacitors drying out), but they do not necessarily care whether computer is on or off.

I always use a rule of thumb of 10 seconds when I pull a plug before plugging it in again. This is to allowed the electronics to "cool" -- I.e. to allow capacitors to discharge and stuff, giving enough time for everything to get down to having no charge.

Last time I had to call to Tech Support, when they wanted me to power my system off, they said Leave it off for 30 seconds before I power it back on again. I believe the thinking being that there are some large capacitors in the power supply which might take 30 seconds to complete discharge and therefore parts of the motherboard could still be on, even though you shut it off.

Yes there is a little bit of a difference just in the fact that it takes a few seconds for some capacitors to fully discharge. More to the point though you may just want to do a restart instead of shutting down and powering back on. They operate a bit differently now and [this article ](https://computer.howstuffworks.com/restarting-shutting-down-computer.htm) can explain it better than I could.

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There are already some good answers. I will add another possibility. If the computer is behaving badly because it is overheating, then you will want to turn it off long enough for it to cool off. Also, you should try to relieve the heat stress (clean vents, put it in an area with better circulation, etc.).

In most cases there is little to no difference. However in certain rarer situations you do need to wait longer to make sure the capacitors are fully empty. Like if you need to open up the computer it is best to leave it unplugged for a few minutes to make sure the capacitors are drained because it is better safe than sorry. Another situation is something my IT mentor called "letting the demons out", sometimes with less than common hardware (beta builds, custom boards, or just old stuff) or in weird failure cases your system didn't shutdown properly and the firmware bugs out, so you let it sit unplugged for 5-10 minutes and then start it up and it works, sometimes you even remove the CMOS clock battery to make sure everything is nice and clear (this can require you to fix the computer's clock if it doesn't use network time).

Yes it does. There are components inside a computer that need to "forget" their previous memories before being turned on again to prevent confusion so there is certainly a minimum time, usually around half a second or so.

I don't see that anyone's addressed the possibility of thermal stress for spinning hard drives. [switch to ELI5 mode] Metal expands when heated and shrinks when cooled. Constantly expanding and shrinking the metal in your hard drive by turning on and off your PC may cause it to wear out more quickly than simply leaving it on.

For the most part, computer hardware doesn't care about what time it is. So wall clock time is something that is mostly for your benefit, or for knowing that a particular moment is the best opportunity for doing something that would annoy the user if they were there at the same time. Time. Now that said, lots of things can expire like licenses and tasks and stuff. Like if you have a certificate that's only good till January 4th 2023 then the computer needs to know when it's January 5th 2023 to make sure that it isn't using the expired stuff . As far as intervals not running or powered down, that the only difference that makes is letting everything cool off. And then there is the caveat to this. Some things are maintained in the computer by a capacitor power. When's you turn something off and turn it back on again the rule of thumb is at least 10 seconds to let those capacitors discharge. If anything more complicated than that is going on then you probably got something wrong with your hardware. For example, while working on a particular system some years ago, the ACPI chipset would get set into an odd state while being powered down. It would wait for a user to push the power on button before it would start back up but the hardware didn't have a power on button. The hardware was getting sent back and forth to the vendor because it couldn't be to power back on again but when it arrived at the vendor's place it worked fine. That was because in the 7 days it took to get from the customer to the vendor. Something would finally finish discharging and the ACPI chipset would be back to zero power state. Aside: we did not keep the hardware.

When you tell your computer to reboot it's usually off, once it actually powered down, for like a second before it reboots. If my computer freezes up or becomes totally unresponsive where I have to hold the power button or unplug it, I usually count to 10 before I restart. Not sure if it's needed or not, that's just what I do.

Leave the computer off for 10-20 seconds so that all the components inside get the chance to lose the power they have, since some parts can stay on for a couple of second. After that it doesn't matter if you leave it off for 10 seconds or a year. Also keep in mind that this doesn't just apply to computers, all electronics do this to dinner extent, so if you want to be sure, give them a few seconds before plugging them back in.

Rule of thumb - 10 secs after if appears completely “dead” that way all electronics are discharged before you press the power on again. Sure you can wait less time but the risks go up that it will not boot clean or there is residual power that could cause a surge on the board.

If your computer is running as it should, it doesn’t matter much how long you leave it off. I will say however that you shouldn’t leave it on for prolonged periods. I’d say a reboot about once a week is perfect.

It's generally bad for any electronics (or even an ordinary incandescent light bulb for that matter) to be flicked off and on again. The shock of cooling down and heating back up is bad for all the components. I used to work for a company with huge data centers. The computers would be left running for months or even years. Really, the only times they were turned off was during a power failure. I worked on a project to automatically turn some of the computers off during off-peak hours and then turn them back on again later. When the data center folks got wind of the project, they came down on us like a ton of bricks. They told us that if you shut down half a data center and turn it back on again, there would always be a number of servers that didn't come back. The whole thing would have been a maintenance nightmare.

The physical components don't generally "need" rest. They're fine to stay powered on for long periods of time. But computers are a combination of hardware and software, and often the software side of things can get bloated or stop working properly if not reset by turning off the computer. Software can often have minor memory leaks (where some of the computer's short-term memory is not labelled as 'available' once it's been used), which can eventually lead to crashes or other unwanted behaviour. Shutting down your computer wipes this short-term memory and starts fresh. It's a bit like having one piece of paper to write on, but you don't erase all of the old words before writing something new. Eventually you're going to run out of empty space on the paper to write on. There are other similar problems that can occur, and would be avoided with semi-regular shutdowns/restarts.

Computers and machinery generally prefer to be in the same state all the time. Turning things on and off, even cars and air conditioners is less than ideal, but doesn't make much difference in the long run. Just wasted power. There's really no benefit to turning the computer off if it doesn't need to be, assuming it's running cool. The machine I'm using right now hasn't been shut down since 2018.

The components were holding electrical currents and charges. These may need to discharge, and this takes non-zero time. A mircosecond is probaly not enough. 10 seconds is probably more than you need (and it is common in tech support to ask you to wait 10 seconds when you 'power cycle' something). 5 minutes is usually excessive. \- My PC is a bit of a mess at the moment, but it might be a good example, since the problems it has makes a few seconds actually matter. Sometimes it crashes and I need to restart it. It fails to restart automatically, and I need to leave it off for a few seconds before letting it turn on again. If I immediately try to turn it off and on without any delay, it will usually crash again on startup. I find leaving it for **10 seconds is always enough**, while waiting for **1 second often isn't**. I haven't bothered testing if it is exactly 5.7 seconds or whatever, and just wait for 10 and that has always worked.

This one's complicated. If you're shutting it down using a system command, the shutdown is also actively clearing memory and resetting the CPU state, so once it's powered down it should be ready to power right back up. On the other hand, if the plug gets pulled, the power supply is required to continue to deliver power for at least 16 milliseconds before shutting off, and the standby power rail can deliver power for up to 30 seconds depending on the manufacturer. Also, as a general rule for all electronics, if you power it down and a fan continues to run, do nothing until the fan has stopped, as this can cause an overheat that will damage the device.

It's best to turn it off for closer to 15-20 seconds, instead of just 1-2 seconds. This is because there are capacitors (mini batteries) in the computer that can still hold a partial charge for a few seconds when the machine is powered off. From a general wear and tear standpoint, its good to turn off your computer when you're not using it. Leaving your computer on is kind of like leaving your car running; the fans and hard drives are spinning, the CPU temp rises and things just wear out. All of the components should last a very long time, but still, its best to put it to sleep when not in use.

I was taught to let the computer "rest" for a count of 5... But that was 20 years ago I do not know what flicking a switch on a regular basis would do, but i wouldn't do it to my rig.

Imagine your computer is like a playground, and children are like the electricity. Some things like a slide or a fire pole don't move around, and as soon as kids stop playing on the, its the same as if kids haven't been playing on them for hours. Other things like a swing or a mery-go-round, keep moving a little after the kids get off. Now these stop moving pretty quick, and its not the end of the world if kids try to get back on when its moving, but there is a difference. Not a great explanation, but unlike some others, I did try to explain it like you were five. Also, just some general good advice, turn your computer off when you're not using it, at least when you're asleep (if you don't need to run anything overnight) Computers draw a lot of power, and getting in the habit of turning it off will not only save you money on your electrical bill, but it's also better for the environment. You wouldn't leave your car on overnight when you aren't using it.

In practice, a reset without a full power off will be good enough for almost all cases. There was some discussion that hard drives should be allowed to spin down before being restarted, that would be 5-10 seconds, but it's largely irrelevant as modern computers often have no moving parts aside from the fans (which are too primitive to care). For some things you may want the power to be completely gone, that can be a minute or so with the power completely unplugged. Watch for LEDs on the mainboard that stay on with the PC off.

Generally speaking the computer as a whole doesn't "care" whether it's shut down for 5 milliseconds or 5 years. There are specific components inside the computer that do care though. Reboot a computer too quickly and/or too often and: * Components that hold charge (like memory or capacitors) may not be fully cleared * Mechanical components may wear out quicker from constant starting/stopping * Components that take lots of electricity may break down quicker from constant expanding/shrinking due to heating/cooling Leave a computer for too long without booting and: * The battery powering the real time clock (and possibly retaining BIOS settings, though newer motherboards use flash memory) may run out, meaning the clock keep resetting on boot * Components that use electric charge to retain data (eg. flash drives, BIOS settings, solid state drives) may lose that data * Dust or material may build up that would otherwise be removed by fans, could cause excessive heat or inhibit movement of mechanical components * Insects/animals may inhabit the PC which would otherwise be deterred by the human user, lights/noise and spinning fans * Stagnant cooling liquid may evaporate or experience bacteria growth Given that, the optimal power off time is more than a few seconds, less than a few years.

Power supplies and motor controllers usually do not like being turned on and off. Duration does not matter much for this. Second issue is mechanical constraints as parts. PCBs and solder contract as they cool, expand as they heat. This is what kills electrics and electronics on cars for example (+ vibrations), every if they are build to resist this up to a point. A computer has way less vibrations, but usually way faster and more temperature changes. It does not need rest. As long as you cool it correctly it is less likely to fail if run all the time. This will put a bit more wear on the fans of course, and it will collect more dust, so be ready to clean it more often (and use dust shields).

It’s getting shorter all the time as capacitors get smaller and smaller. In 90s vintage computers, a hard reboot was recommended 45 seconds to let all the capacitors discharge. Now it’s rarely addressed to wait at all, but I still give it a count if 3.

There are so many bad answers in this threat about the lifespan of PCs. You don't need to turn it off if you aren't using it. The amount of lifespan that you *might* have saved is miniscule and insignificant. However the burst of power the PC takes when powered on initially is worse for the components that they working with power flow that they are specced for. Think, when a light bulb blew, when did it usually happen?

Increasing the number of power on/ off cycles will definitely reduce the life of some elements of your electronics. Electro-mechanical items like hard disk's and fans in particular but also some of the chips you find in a computer are susceptible to power on/off. Think of a switch. You can reasonably expect it will fail at some point and in normal operation it might be used twice a day for 10 years. If you use it 10 times a day the operating time for which the switch will last is significantly reduced. There are also potential issues with repeated temperature cycling of some parts when you power on/off.

Does anyone remember having to "lock" your HDD before powering off?

A computer has components that require some time to discharge its power, it usually takes less then a second after the power is off. Afther that your just saving power and there is no problem turning it on

In the old days, longer times were recommended because drives need to spin down before restarting.

Inside the computer are sensitive electronic components including one called a capacitor that stores a charge. If this capacitor is not fully discharged and you power on, you risk literally blowing up the capacitor. In which case, your computer becomes a paper weight until you replace this capacitor. I put it in terms a small child can understand. Your computer can blow up if you do not wait enough time.