How long can a computer safely run?

I apologize if this is a simple or stupid question but I was asked this by my wife and I don’t have an answer. I know that turning a computer on and off “stresses” the computer more than simply leaving it run. But…how long can one safely leave a computer run? She will be leaving town for an extended period of time (10 days) on business and she asked me if it was OK to leave an unattended computer (MacPro with multiple monitors) running for that long. Answers to this question + a link or two that I can point to to back up my response to her? Thanks.

Computer servers are often left running for months or even years at a time. Ten days is no big deal.

The bigger problem, rather than the wear & tear, is that leaving a computer running that long unattended is just a waste of electricity.

My rule of thumb is to let personal computers sleep overnight or over weekends, but if going away for a week, just turn it off.

Credentials: I can’t cite any URLs at the moment, but I manage servers for a living, and in the past I used to do desktop & notebook repairs for Apple.

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Your computer will be okay for much longer than that. Computers are routinely left on continuously for years at a time.

I use a Mac Mini as a media server. My previous one served that purpose from 2008 to a few weeks ago, and hasn’t been off for more than the occasional hour (I only shut it down during thunderstorms). Reboots were maybe twice a year.

Turning a computer on and off stresses it a bit (thermal cycling). But the reduction in lifespan is usually not noticeable, so if you’re leaving it on for 10 days to avoid the stress of turning it off and on once, you’re taking the more expensive option: you’ll spend more on the cost of power to leave it on than you save by stretching the computer’s lifespan by a tiny amount.

Harro de Jong

I never turn off any desktop computer I own. I have older model mac pros that have been on continuously for 10-15 years. I have a trash can mac pro that has been on continuously since I purchased it, except for the continual “power switch” reboots because the thing is so unstable with a bunch of lightening gear attached.

You don’t need (nor are you likely to find more than a few) articles to back-up claims about leaving a computer on is harmless. It’s common sense. Turning on and off a computer requires more power (and puts more wear & tear on it) than just leaving it on. Of course that’s within reason, but it’s just like any other electric device or a car.

The fact is, the Mac goes into a deep sleep mode that is all but shut off anyway. Turning the Mac off doesn’t conserve any power at all vs. letting it go into deep sleep mode unless you physically unplug it from the power outlet.

That being said, there’s no reason to leave it on for 10 days if you’re not even there. Power surges, Brownouts and Blackouts can destroy a computer—and it’s easy to avoid. Turn the computer off.

I tell clients to go with the convenience more than worry about the stress on the computer: putting it to sleep is better than shutting down, as you can leave your work and be right back to it as it was. Shut it down if you’re going to be away from it for a few days.

My machine is running all the time, with screens shutting off after 20 minutes.



I don’t think that it matters much either way.

In favor of leaving your computer on all the time: Heat cycling causes metal parts to expand and contract. This can lead to cold (i.e. cracked) solder joints on your mother board, especially those around the power supply which see large extremes in temperature. Also, mechanical components, such as on/off switches, can eventually wear out. Capacitors are somewhat fragile and they tend to blow right when you turn a computer on from the surge in current.

On the other hand, some components, such as rotating disk hard drives, reach the end of their expected life-span faster is they are left on all the time. If a hard drive is rated to last X number of hours, if you leave it on all day and all night, instead of turning it off at night, you are doubling the hours per day that it is on, thus theoretically accelerating the arrival of the end of its life by a factor of two.

Magnetic media’s natural enemy is heat. The more heat you expose magnetic media to, theoretically, the more you hasten its demise.

So, there are arguments on each side of the debate.

A number of years ago the head of my user group wrote a paper about all this. He called engineers at Apple, Quantum hard drives, and a bunch of other illuminaries. What they said was interesting. The concept of leaving a computer on 24/7 is a holdover from large mainframes. Mainframes used to live in air-conditioned clean-rooms, and they were over-engineered. They were designed to be left on 24/7. Personal computers aren’t really designed for that. Nowhere in any user manual, or in any technote will you find a recommendation to leave your Macintosh computer on 24/7.

However, nowadays technology is such that computers, especially Apple computers, will usually last for many years without a problem no matter if you turn them off at night, or leave them on 24/7. Chances are excellent that all of our Macs will never die. Instead, at some point we will simply want a new (or at least newer) Mac, and our old Mac will be replaced with a newer, faster, better model, and retired to a closet never to be used again.

So turn yours off or leave it on as best suits you.

I do suggest that you use a UPS, as it seems to me that folks who have a good UPS tend to have way fewer problems than folks who do not, including having Macs that seem to last forever. I also recommend that you maintain a meticulously updated backup, because if anything dies in your Mac, it’s most likely to be your hard drive. Especially if your Mac is over 4 years old and you have a rotating disk hard drive.

As of several Mac OS revisions ago, open applications and documents (even unsaved documents) survive a shutdown and restart: you can continue right where you left off. So that’s no longer an argument in favor of leaving the machine running.

Harro de Jong

:slight_smile: I guess I must have turned that off at some point… I will have another look, thanks Harro!

I never turn my computers off, or let them sleep. I do let the screens sleep though. Currently my MBP “uptime” is 32 days 6 hours.


I too never turn them of or allow them to sleep. My external hard drives put themselves to sleep when not used for a while. The screen automatically goes to sleep, or I manually do it with Ctrl-Shift-Eject. I think the longest my iMac every went without re-booting was 118 days. That was several years ago. These days some sort of a software or network snafu or installation will have me re-boot at least every 2 weeks.

Back in the day, late 1970’s, I had several computers that had some socketed chips, usually memory. It became apparent that cycling the power off and then on each day or each use, caused the socket chips to walk themselves out of their sockets. It was SOP to open the machine up and press down on all the chips to force them to be seated back in their sockets. That experience was all I needed to see results of thermal changes on electronics. Since I have started to always leave my machines on, I’ve never had an electronics failure. Hard drives wear out eventually no matter what but that’s a mechanical issue in most cases.

I run Folding@Home on all of my macs that can usefully do so, and have for a very long time. They stay up 24/7 running at full tilt, never allowed to sleep except in heat waves (for my comfort, not theirs). With the possible exception of the G5 tower that leaked coolant over, and destroyed, so much of the machine that it was declared unrepairable and sent back to Apple engineering as a curiosity, I’ve never had a problem.

I run minis on their sides for better airflow though, since they run cooler that way. I forget the numbers, but I tested several with Bresink’s Hardware Monitor at some point. (By on their sides, I really mean on their fronts, since it’s so handy to have the ports sticking straight up.)

It really doesn’t make all that much difference. I remember Windows XP taking five to ten minutes coming up from off and logging in. Turn the system on, and get coffee. In the old days, spinning disks and power supplies would churn even when the computer was “asleep”. Powering our computers off over night use to save hundreds on utility bills because the CRT monitors weren’t heating the building. Plus, the power supply would sometimes over heat and blow.

Now computers run cooler. SSD don’t spin and wear down. At the same time, my Mac can come up from a cold start in less than a minute and most of the programs I use pop back up right where I left them.

So, it’s up to you. Leave your computer on, and it’ll put the screen and disk to sleep after a few minutes, but still receive mail and notifications. You’ll save a few seconds not waiting for it to boot and the programs coming up. Long enough to be bored. Not long enough to get coffee. Turn the computer off and you might save a few pennies in power.

Personally, I leave mine up and runnIng, but that’s mainly because I just don’t bother to turn it off.

I think the main reason we used to worry about turning on computers is because of the peak power needed to start a hard drive spinning. Not really a problem anymore.

Me, it is mainly the batteries that worry me. I have two MacBooks that I leave on for most of the time (often even with the lid closed, thanks to the utility Nosleep). But I typically shut them down when I leave them unattended for prolonged periods because a couple of years ago I’ve had one MBA whose batteries spectacularly failed, and I don’t want that to happen when I’m not there.

I hadn’t considered this, as I don’t use a laptop, but my comments were based on desktop iMacs (and older Macs). I think if I had a laptop I would not be leaving it on unless a task was running. Thats my 2 cents.