Question Why exactly is sudden power loss so bad for PCs? is it just the threat of data corruption, or is there another worse consequence?

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abufrejoval

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hedwar2011 said:
Sudden power loss can send shock (electrical surges) through a computer if not connected to a proper surge protector or battery backup. It is essentially like a component getting hit by static electricity just on a much larger scale.
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I'm somewhat skeptic you'd see such surges if someone were to yank the power cable, even if with stabelizing circuitry and capacitors I could imagine some voltage lines might "surge during death throes".

But sure, power cuts are rarely just cuts, but come as the consequence of a significant event which has power "misbehave" in every direction before some fuse shuts it down.

I've shut down misbehaving PC for decades, always with some trepidation, especially once I started running Unix and other more sophisticated operating systems. On earlier microcomputers like Apple ][s or even in the DOS era, a quick power toggle was just another way of doing a reset, as the original IBM PC didn't even have a button for that.

But I can't really recall anything beyond loss of data ever practically happening, even when I was running RAID6 without a BBU or SSDs without capacitors, where the risk of terminally inconsistent data isn't just theoretical: perhaps I've been very lucky, but laptops also helped the industry to view power loss as less of an exception.

Generally I've noted a marked improvement in how PC have handled crashes, resets and power cuts, in earlier days a long file system check on a reboot was practically guaranteed, but today even the explicit checks I tend to hardly ever report and need for that.

Yet I certainly wouldn't want to cut power from PCs to test just how well and how long they manage to survive that: perhaps someone at Tom's hardware would want to volunteer?
 
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stonecarver

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And if your system makes it through a power loss due to lightning or natural reasons. Or where I live it's most likely someone crashed into a utility pole and killed power.

The in rush of power when it comes back on is a killer of PC as well.

Have you ever turned on a valve to a garden hose that was empty just full blast. That hose will whip until the water has pressurized, it's the whip / in rush of voltage that sometimes does damage as well.
 
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Order 66

Order 66

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hedwar2011 said:
Also you have to consider ESPECIALLY if the power failure is disaster or accident related, it's likely that the power doesn't drop straight out but flickers a few times and then stays out. That alone can do weird things to a computer if it's not set to stay off when the power fails.
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what were to happen if say, the power cord was suddenly yanked from the wall?
 
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USAFRet

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Order 66 said:
I cannot imagine the damage that a lightning strike would do to a plugged-in PC. Would it fry it or does it depend on other factors?
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Real world experience:

Summer 2020, working from home due to COVID.

3 groups of PC equipment, on 3 different good quality UPSs.
Pod A, B, C



Rain, rain, rain...BAM!!
Lightning strike in the yard, as close as I can figure.
Basically, whole house rebooted.

UPSs started beeping.
Everything came back online.
Sort of

Damage:
Pod A
Main PC - ethernet port (switches and router, no damage)
That PC still works, with a PCI ethernet card.

Pod B
Printer - ethernet port (switches and router, no damage)
Denon AVR - HDMI port (the connected TV, no damage)

The PC in Pod A and Printer in Pod B were separated by 2 switches and a router.

Pod C
Nothing at all


Other things:
Years ago, my ex had an Invisible Fence installed.
The control box was still in the garage, unplugged. The box cover was singed and blown halfway across the garage.
The wire is still in the ground, and that evidently carried the signal.

Now, the Twilight Zone moment:
I have a nice laser level. Battery powered. It was in an upstairs room center of the room far from any walls or outlets. It was OFF, had been OFF for a week or so.
I go upstairs later - hmm...whats that red glow.
It was ON. Apparently, enough electricity through the air to turn it ON.


Electricity can follow strange pathways.
And anyone who says "Oh, I always disconnect everything when there is a lightning storm".
No you don't.
Routers, switches, TV, stove, microwave, etc, etc.

Plus, there is not always "Lightning within 5" notification. For every storm, there is a 'first strike'. This was that.
All there was before was just rain. If I unplugged everything, every time it rained...it would be off more than on.
 
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Order 66

Order 66

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USAFRet said:
Well, I'm still vertical and breathing....apparently not...;)
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My family (myself included) is horrible about this, we never disconnect anything during storms, even though we probably should. Also if a device has a 3rd prong on the plug into the wall, would that help prevent it from getting fried, or what is the third prong for?
 
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hedwar2011

hedwar2011

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USAFRet said:
Well, I'm still vertical and breathing....apparently not...;)
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I feel you.

Real world experience from about 6 years ago now. Long story short a micro-burst (tornado) hit our house and caused what I consider a localized EMP. It tore up our kitchen (with me in it, no injuries), fried our microwave, rendered 2 cars unable to be started for like 2 days afterwards, and also ignited a long dead overhead light bulb installed by our electric company.
 
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helper800

helper800

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The most damaging types of events related to power a computer can experience are brownouts, sudden loss of power while firmware, BIOS, or drivers are being updated, and sudden bursts of high current like from lightning. Lightning can cause all sorts of issues but it really depends on where it strikes.

If a strike affects ISP equipment then a burst of that electricity can go into your modem => WAP => PC. The way to protect against this kind of surge would be a surge protector with coaxial and ethernet ports that can filter out the surge before it hits the modem, or at least the PC depending on the surge protector. Of course having all your devices be wireless will at least protect them from being hardwired into the WAP or switch.

With brownouts you need a decent UPS unit to protect against them. Brownouts are potentially more damaging than surges for electronics. The same goes for sudden loss of power during delicate firmware, BIOS, and driver updates, you need a decent UPS.
 
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Order 66

Order 66

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helper800 said:
The most damaging types of events related to power a computer can experience are brownouts, sudden loss of power while firmware, BIOS, or drivers are being updated, and sudden bursts of high current like from lightning. Lightning can cause all sorts of issues but it really depends on where it strikes.

If a strike affects ISP equipment then a burst of that electricity can go into your modem => WAP => PC. The way to protect against this kind of surge would be a surge protector with coaxial and ethernet ports that can filter out the surge before it hits the modem, or at least the PC depending on the surge protector. Of course having all your devices be wireless will at least protect them from being hardwired into the WAP or switch.

With brownouts you need a decent UPS unit to protect against them. Brownouts are potentially more damaging than surges for electronics. The same goes for sudden loss of power during delicate firmware, BIOS, and driver updates, you need a decent UPS.
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How expensive is a UPS? Looking on PCpartpicker, there is a UPS listed for $19k, but I am not sure if they are supposed to be that expensive.
 
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