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I was wondering: What's the difference between shutting down the computer and shutting down the hard disk?
Aren't they the same thing?
That is: I can't use the computer if the hard disk is shut down. If I shut down the computer, isn't the hard disk shut down along with it too?
Pacerier
Posted 2011-10-20T10:29:39.040
Reputation: 22 232
14
"Turn Off Hard Disk", is poorly worded in the Windows 7 power properties, the drive is put into "standby", not actually turned off. The drive is "spun-down" to save energy and wear on the motor bearings. On supporting laptops it is put in an even lower standby state. Like ranon said, it occurs when the system or a controller/driver deems that the user is idle for disk activity. It is an independent item, for example the hard drive can go to sleep without the screen saver or screen-off occurring.
If the drive is accessed, the drive wakes back up, The motor spins the platters back up to speed, and then any access to it is returned. You can tell it went to sleep by hearing it spin back up, or because of the seconds of delay you get when trying to do something.
Hibernate is to save the entire present state of operation by moving the ram to disk, and putting the computer into the "off" state.
A computers main Ram needs constant power to keep the Data in it. By shifting the contents of the ram to disk, the contents can be returned to ram. That way even though the ram was empty, the state that the computer was in can be returned mostly. Returning from Hibernate, the contents of the ram are put back in from the hard drive.
Psycogeek
Posted 2011-10-20T10:29:39.040
Reputation: 8 067
4I would have said it is purely to save energy/battery, not wear on the motor. It is my understanding that spinning down and spinning up hard disks can actually increase wear and reduce the life of the hard disk. (?) – MrWhite – 2011-10-20T11:00:44.773
2Yes, getting the momentum going on the flywheel :-) is the hardest load for the motor. there is a balance between bearing wear and motor load. On desktops i like to allow the disk to sleep only if there is not going to be access for a long time. so I set for 45-60 min – Psycogeek – 2011-10-20T11:04:24.273
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"turning off the hard disk" means turning it off while your computer is running, but there hasn't been any hard disk access for some time.
Hibernate stores your main memory's contents and cpu state to hard disk and then shuts down your computer completely.
Jens Erat
Posted 2011-10-20T10:29:39.040
Reputation: 14 141
I mean what's the difference between shutting down the computer and shutting down the hard disk? – Pacerier – 2011-10-20T10:39:52.770
@Pacerier Shutting down the computer means shutting down the power to, simply put, "all" components. That's why you need to save your RAM contents to the hard drive, otherwise it will be gone. On the other hand, if you just power down the hard drive, the RAM will still be powered. – slhck – 2011-10-20T10:41:54.657
@slhck Do you mean that we can shutdown the C:\ hard drive and still use the computer? What will happen to the windows stuff under C:\Windows – Pacerier – 2011-10-20T10:47:19.487
With just the hard disks "turned off" (which obviously saves battery) there will be a noticeable delay when you then use the computer again after a period of inactivity, as the disks need to spin up again. – MrWhite – 2011-10-20T10:50:02.337
Usually, your C: hard drive will not get shutdown because there is regular access to it (there are always lots of system processes running, logging, ...). If it gets shutdown, it will be restarted when accessed next - you might feel some little latency as restarting a hard drive takes some few 100 msec. Usually only "data drives" get shutdown. – Jens Erat – 2011-10-20T10:50:49.057
The hard disks will only spin down (turn off) when they have not been accessed for a period of time eg. 30 minutes. This does not turn the computer off. If you then try to access the hard disk (or the computer does some maintenance in the background) then the computer will automatically spin the disks up again (slight delay). – MrWhite – 2011-10-20T10:53:22.910
Thinking about my laptop, als your system drive powers down sometimes - you will hear some "clicking" noices with some hard disks. – Jens Erat – 2011-10-20T11:06:44.770
Hard drives use a permanent form of storage via magnetic media. The contents aren't lost just because power is removed from the device. Flash memory works in a similar manner. The DRAM (main memory) in your computer requires power in order to retain its contents. – Anthony Giorgio – 2011-10-20T11:40:31.060
@w3d When you say that "if I try to access the hard disk", you do mean that as long as I do not open any files in that hard disk (i.e. I'm simply working with programs that are already opened) then I am not accessing the hard disk? – Pacerier – 2011-10-20T14:24:20.323
@Pacerier: If you open or save files or view the directory structure in explorer for instance then the hard drives will spin up. However, some applications might save temporary files in the background and Windows itself will perform certain disk maintenance tasks in the background, so whether the drives remain 'off' whilst you are actively using the machine might be dependent on other factors. – MrWhite – 2011-10-20T15:29:39.637
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When Windows shuts down a hard drive, it just stops the drive's platters from spinning. The filesystem is not unmounted, although your programs are still running, and the disk's write cache is purged. However, Windows knows that any attempts to access the disk will require it to be powered back up, so you will notice a delay if you try to use the computer after the HDD is shut off.
When you actually go Start -> Shut Down, Windows unloads all running processes, purges all disk write cache, and then unmounts the filesystem. And then your entire computer shuts off.
The big difference between the two is power consumption. Your computer is using more power then in a standby state when the hard drive is shut off (since your CPU and RAM and Motherboard still need full power), although the computer may use significantly less power than it did before. Turning off just the hard drive also allows some tasks to continue running, so long as they don't require hard drive access.
Breakthrough
Posted 2011-10-20T10:29:39.040
Reputation: 32 927
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When computer starts:
Maxim V. Pavlov
Posted 2011-10-20T10:29:39.040
Reputation: 1 432
Are you saying that theoretically when the OS is already loaded, we can wipe out the HDD since the OS is already in memory? – Pacerier – 2011-10-20T14:17:47.867
Yes, and the moment the OS will require something from the drive it is most likely to fail. Wiping is only possible theoretically though, since most OS's (there are basically two of a kind) will be constantly spinning the system drive. My Windows 7 machine though seems stop even the system drive sometimes, but I may be wrong. – Maxim V. Pavlov – 2011-10-20T16:12:36.900
Actually yes you can wipe the drive and it keeps on running. I learned that the hard way. The drive was on the blink but still working. Startup was very slow. Then one day the drive just died but the computer ran for some time until it needed something from the now dead drive. – John Smith – 2011-10-20T16:13:26.697
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There's no context specified in the question, but my experience has been that non-technical people often refer to "hard drive" when they actually mean the entire computer. It's highly probable that they are using that particular terminology because the believe that it sounds more technical than just saying "the computer". In reality, while providing technical support, when a user refers to the "hard drive" it's a red flag that that you are dealing with someone very little technical know-how, and you'll have to make sure that any explanations that you give them are simplified as much as possible.
Dave
Posted 2011-10-20T10:29:39.040
Reputation: 121
"sleep" saves the current state in RAM, "hibernate" saves the current state to hard disk. Both result in the computer being powered down, but "sleep" uses some battery power, but is quicker to power up again. – MrWhite – 2011-10-20T10:46:30.797
@w3d I mean I'm pretty clear about the differences between to sleep and to hibernate, but confused about the RAM and hard disk – Pacerier – 2011-10-20T10:48:38.253
You can't use the computer if your monitor is turned off, and if you shut down the computer the monitor shuts down along with it too. This doesn't mean that turning off the monitor and turning off the computer is the same thing. – Thomas Bonini – 2011-10-20T14:23:35.447
@AndreasBonini ok.. though we can of course use our computers even when the monitor is turned off. – Pacerier – 2011-10-20T14:27:35.623
2You might find live CDs interesting. You can have the entire OS running normally without using the hard drive at all (and if you can manage to cache the entire CD in memory, you could take that out too). – Brendan Long – 2011-10-20T17:32:27.693
I've seen the term "hard disk" used to mean not the hard disk, but the computer box (in contrast to monitor, keyboard, etc). Perhaps that is part of the confusion? (As Dave wrote in his answer.) – Thomas Padron-McCarthy – 2011-10-21T07:30:19.267
@Thomas I guess so it is – Pacerier – 2011-10-22T14:26:44.230