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Hard-drives have a definitive “on” status (they spin up, the heads move, and they use more electricity than when they are “off”). The same goes for a computer (fans and lights activate), monitors (relays click, electron-guns fire/LEDs light), and so on. But what about SSDs?

A hard-drive requires the disk to be spinning and the head to have power in order to read or write, but an SSD is more like RAM when it comes to reading and writing; it requires no movement, just a direct electrical write. Further, unlike RAM which needs to be continually refreshed to retains its contents, SSDs retain it after one write like hard-drives (SSDs are the best of both RAM and HD).

Therefore, do SSDs have a definitive on and off state or are they just a lump of electronics that sits there doing nothing until an actual read or write operation, and only use electricity then?

(Power-management may complicate things a bit since most devices are “turned off” while they still retain a trickle charge. Therefore, most devices are either “on”, “off”, or in “standby”. This doesn’t change the question though, since I’m asking about normal “on” usage, not standby.)


Update:

Thanks for the responses (I’m familiar with how electronics work; I recall all too clearly some of my uni exams), but all the current answers miss the crucial point to the question: a device (eg HD, monitor, etc.) that is “on” uses significantly more power than when it is off (or even standby).

Does this apply to SSDs as well?


Note: I had the thought that SSDs (including regular flash drives and memory cards) do seem to be “always on” in that they are immediately accessible. That is, unlike a hard-drive or optical drive which can spin down or at least take a moment to access when they reduce power, files stored on a flash drive are always instantly accessible no matter how much time has passed without it being accessed. (I suppose that could lead to the question do SSDs turn off (eg to conserve power) instead, but that would be a separate question, if even required—which it is not).

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2 Answers 2

up vote 13 down vote accepted

Digital electronic equipment in computer systems all have a definite "on" state. Even if there is no mechanical moving parts in the machine, digital circuits still have various states. Every action performed by these digital circuits are essentially a transition from one state to one or more other states. If there is no power going to these circuits, they are off, which means essentially (to use an analogy) trying to get the computer to talk to it and get a response would be like trying to have a conversation with a dead corpse.

When a computer turns on, all digital circuits go through an initial state. It's typically called "reset", where all the random electronic charges in the materials are cleared out and the circuit enters a stable initial state, ready to perform its function when state changes are triggered via its input(s). This would be analogous to a HDD spinning up. It's changing from its resting state to a state of readiness.

So, yes, they have a definitive on/off state. They have to, since it's not just the storage medium but all the supporting electronics that allow us to read and write to them.


Update for the OP update

Yes, it likely uses less power when off. The thing is that it does not have to power a motor like a HDD does. A HDD will spin down when idle to conserve power (if you set it to). The only reason to keep it spinning is so that you don't have to wait for it to spin up before you can read data, which can take a second or two. But with a SSD, there aren't any concerns with things like that. It will consume power so that it may accept read and write requests, but it likely won't be consuming as much power as when it's processing read and write requests, simply because it is using less circuitry, and therefore, using less electricity. It will not be using any electricity when turned off, because (like all the other components in your computer), the motherboard would have told your power supply to cut off electrical current to the device. When turned off, unless you have a very old computer, the only electronic device in your machine to receive power will be the motherboard, and only just enough to monitor the power button. The power output to the drive will be outputting very little, if any, electrical current, in this state, though.

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> The thing is that it does not have to power a motor like a HDD does. … But with a [sic] SSD, there aren't any concerns … It will consume power so that it may accept read and write requests, but it likely won't be consuming as much power as when it's processing read and write requests, simply because it is using less circuitry…. Yes, but I mean relative. Obviously an SSD uses less than an HD, but does an SSD have an “on” state in which it uses significantly more power or does it only need power to do reads/writes, ie, does it need much power when it is idling the way an HDD does? –  Synetech Aug 27 '11 at 0:55
    
@Synetech It's not a grammatical error to say "a SSD" if you read it "a solid state drive". :) Anyways, as far as when it's idling, yes, it does need power to maintain its state, however, it will ramp up on the power usage when it's doing read/writes. As far as how much, I don't know, as I've never tested it. But it will use power. It's not the same as "off". That's what I'm trying to say. –  Ben Richards Aug 27 '11 at 1:03
    
> It's not a grammatical error to say "a SSD" if you read it "a solid state drive I’m too lazy for my cat, uh, I mean to say the whole thing. :-) > But it will use power. It's not the same as "off". I suppose that makes sense. As a somewhat poor analogy, I imagine SSDs to be a little like paper and pencil (or stone and chisel): they are inert when not being used. A better analogy is a light-bulb or Morse-code terminal. It uses power when sending a signal, but not when idling. –  Synetech Aug 27 '11 at 1:15
    
@Syntech Well, the controller circuits on the SSD still are operating even when the drive is "idle". It's more than simply a medium, like I said before. Since it's not physical in any sense of the word, it takes electricity to create and transition between states. It's more like having a regular cell phone turned on but idle, as opposed to turned off or in a call. –  Ben Richards Aug 27 '11 at 1:21
    
I like that analogy, and the line It's more than simply a medium sounds good too. –  Synetech Aug 27 '11 at 1:25

They definitely turn on. Specifically, the disk controller is required to be on and active.

You'll notice this when you google the infamous Sleep/Hibernate BSODs. Sandforce controllers were particularly prone to this. What would happen is sometimes the disk controller would be shut off during sleep, S3, and never wake up, forcing a reboot. In other cases, a reboot didn't even do that, forces an RMA.

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