In a recent post I mentioned that I leave my PC on all the time. In response to that, Dreadjaws said:
I confess to be entirely ignorant about this subject. Some people swear to me that there’s no benefit in shutting down the PC every day, while others say there is. At work the machines are turned on 24/7, but at home I tend to shut my PC down when going to bed. While, being fair, the primary reason I do this is that the PC is in my bedroom and the bright lights and occasional fan noise annoy me when I try to go to sleep, I would really like to know what’s the deal.
Doesn’t it cost more to keep the PC on all the time? Or is the act of booting it somehow more costly? What are the real benefits for each?
I’ve been wondering this for years.
Back in the 80s, it was objectively better to shut down for the night. The PC couldn’t shut down those energy-sucking CRT screens, which was a big part of the energy drain. Certain systems might be smart enough to blank the screen, but that just means the monitor was working very hard to display nothing. If you looked at a supposedly “black” screen in a dark room you could tell it was still on. That electron gun was still firing, still being guided by rapidly-shifting magnetic fields. The hard drives kept spinningHow many people remember the days when you had to park a hard drive?, the CPU kept twiddling its thumbs, and the machine used nearly the same amount of power as when it was in regular use.
Over the decades we’ve replaced the wasteful CRT with LCD panels. We’ve added sleep and hibernate modes to devices so they can enter a low-usage state. On top of that, a lot of components need less power overall. At some point it’s possible we crossed a threshold to where it’s better to just leave the machine on.
Machines burn a lot of power when booting up and shutting down. Rumor has it that shutting down apps on your phone can make your battery usage worse because the per-app startup and shutdown is more expensive than the idle. It’s not unreasonable to think that perhaps the same might be true on a desktop machine where loading a program involves spinning a physical disk at 7,200 RPM and moving the physical head around faster than the human eye can see.
I’m not sure why it takes Windows fifteen seconds to shut down, but it does seem to get the machinery spinning. Likewise, starting up is a big deal that puts more stress on the machine than you see when the machine is in regular use. And don’t forget to include the cost of starting all those programs again. If it takes another minute of spinning drives to open up Adobe BloatWare 7, Microsoft MemHog 2016, and your 15-tab web browser session before you can begin work, then all of that is also part of the overhead of shutting down. It’s entirely possible that a full cycle shutdown at night and startup in the morning will burn more power than if you just let the device sleep overnight.
I suppose the numbers might depend on usage time. I begin using my computer the moment I wake up and I keep using it until I go to bed. I do this every day. Even in best-case conditions where I get a full 8 hours of sleep in a row, we’re comparing a shutdown + boot cycle against 8 hours of sleep mode. On the other hand maybe you only use your machine for work. It only needs to be on from 9 to 5 on weekdays. Maybe the longer intervals of downtime tip the scales and make it more efficient to turn the machine off.
But before we get too excited about measuring electricity usage, let’s not forget the ravages of entropy. Those shutdown + boot cycles get the physical parts moving around, which increases wear and tear on the hardware. Cars have a similar trade-off. Idling when you’re not using the car is a waste of fuel, but starting an engine is really hard on it. People come up with these vague rules like, “If you’re going to drive again in less than five minutes, then it’s better to leave the engine running.” Of course, that “five minutes” figure is an arbitrary round number and the true “break even point” for shutdown probably depends a lot on how big the engine is, how old it is, and how sophisticated replacement parts are. How much energy goes into a replacement starter motor? The energy required to replace a modern starter is going to be astronomical compared to the gas burned while sitting idle for a minute or two. Certainly it would be bad to turn off the engine for ten seconds, and leaving it running for an hour would be a huge waste, but good luck finding the crossover point.
So What’s Best?
On one hand, maybe you should leave the machine on rather than pushing the device through a daily power cycle that wears out the equipment more quickly.
On the other hand, most hard drives outlive their usefulness. A majority of drives end up in the trash not because they failed, but because they’re obsolete. If a drive is likely to operate for 12 years but it’ll be obsolete in 5, then the extra wear and tear doesn’t matter. Even if the extra boot cycles cut its life expectancy in half, it’ll still last long enough to be retired before it dies.
On the other, other hand, we’ve hit a plateau in terms of hardware and our machines are turning over more slowly than ever before. My current computer turned 5 this year and it’s still running modern games like a champMy graphics card is getting a bit long in the tooth, but I can’t afford a new one in this market.. The point is that we’re no longer throwing these things away every two years. You may indeed still be using that new hard drive in a decade, and maybe that extra wear and tear matters.
On the other, other, other hand, waiting for a boot-up each morning is a waste of your time. A desktop PC burns anywhere from 75w to 200w, depending on what you’re doing with it. In sleep mode, the power usage goes down to ~5. Maybe sleep is more efficient than off, or maybe off is better, but either way we’re only talking about a couple of wattsYour PC still draws about 1w even when its off, so it can power itself on when you push the button.. Sure, maybe you’re willing to sacrifice a couple of minutes of your day to save some tiny handful of watts. But if that’s the case, then save up those minutes until the end of the week and spend them washing clothes by hand or hanging your laundry up to dry instead of using a machine. You’ll save about a hundred times more than the power savings you’ll get from optimizing your PC power policy.
On the other, other, other, OTHER hand… who cares? It’s easy for us nerds to get distracted by trivial problems and waste time optimizing things that don’t matter. The fact that there’s no clear answer between shutting down and leaving on means the overall difference is probably very small. All of this is a drop in the bucket compared to the really big stuff. If you’re worried your on / off policy might be wasting some absurdly tiny bit of power along the way, just turn off your air conditioning for one day in the middle of summer. Sure, it’ll be miserable around the house that day, but you’ll save enough power to offset your slightly wasteful PC usage for several years.
On the othermost hand… I’m still curious where the crossover point might be. Is it worth shutting down for eight hours? four hours? One hour? I don’t think the answer will alter my behavior, but I’d really like to know anyway.
 How many people remember the days when you had to park a hard drive?
 My graphics card is getting a bit long in the tooth, but I can’t afford a new one in this market.
 Your PC still draws about 1w even when its off, so it can power itself on when you push the button.
So what happens when a SOFTWARE engineer tries to review hardware? This. This happens.
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