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How Do Hard Drives Work?

  1. Aug 17, 2011 #1
    Actually, I understand the basics of how hard drives work, my question is more specific. I'm curious as to how a computer's hard drive can simultaneously delete files, read files, and download files all to/from different places on the hard drive.

    It can't just be due to a fast-moving head, it can't possibly move fast enough to do all those things for multiple files at the same time, right? If it can, how in the world did engineers get a hard drive to read and write to many different places so quickly?

    Our ability to create things just boggles my mind!
  2. jcsd
  3. Aug 17, 2011 #2


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    It helps that the read/write head actually has multiple heads. They all move in unison, true, but one can be reading while another is writing.

    Beyond that, though, yes. They are just incredibly fast.

    You can read a little about it: http://en.wikipedia.org/wiki/Hard_disk_drive#Data_transfer_rate

    BTW, they actually only have 2 actions: read and write.
    Deleting is simply removing (overwriting) the pointer to the file. It doesn't actually touch the file.
    Downloading is not a hard drive thing. That's a network thing.
    Last edited: Aug 17, 2011
  4. Aug 17, 2011 #3
    Most quick actions are done from within RAM where there are no moving components. Then when speed is not so critical it writes to the HD. However most HDs are now at least 7200RPM which is quite fast.
  5. Aug 18, 2011 #4


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    Hard drives, at least the ones used on PC's don't do that anymore. Because of the high track densities and the fact that servo patterns are created by other devices, the tracks from surface to surface are no longer lined up. It takes longer to switch heads and reposition the head to track center than it does to step across a surface by 1 track and recenter the head.

    With average seek times at 10ms or less, and at 7200 rpm (or in some cases 10,000 rpm), the total seek time isn't too long and the drives can random access fairly well. There is also read ahead and write behind caching going on in the drives and also in the computer (depending on the OS). The main improvement has been in streaming transfer rates because of the increasing bit densities.
  6. Aug 22, 2011 #5
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  7. Aug 23, 2011 #6
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  8. Oct 6, 2011 #7
    Besides how this mechanism works, I have another question about reading two or more files simultaneously from a hard drive.

    Isn't this bad to burn a DVD from an HDD and at the same time try to open different files and listen to music and ... from that same drive?

    I say that because when I'm burning a DVD from my external drive and try to play a video file or copy from my HDD at the same time, the Writing Buffer decreases to zero or the video files I try to play have little interruptions when playing.

    I don't think it's because of my system components. my external HDD is USB 3.0 and I have Windows 7 HP and a Dell XPS 15 L502x with Core i7 and 6 GBs of RAM and my burning software is Nero which is a professional tool. Is this normal?

    I'd be very thankfull if someone could help.
  9. Oct 6, 2011 #8


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    A hard drive can't do multiple reads simultaneously. It's reading data from one location at a time. It can anticipate further reads from that same area later with read ahead buffering to reduce the amount of random accessing. A hard drive's data rate is much slower if it has to do a lot of random accesses.

    Depends on the data rate required to burn the DVD versus the effect data rate of the HDD if it's doing a lot of random accessing, but yes, it's probably a bad idea. The DVD burning program should set it's priority higher than normal (you can check this with task manager), so that the music or video would get interrupted, instead of the DVD burn process, which I think needs to be continous. If you have multiple hard drives, then burning the DVD from one hard drive while watching a video from a different hard drive should not be an issue.
  10. Oct 12, 2011 #9
    Thanks a lot rcgldr. i hope it would be helpful to use priority options of task manager. There is also some third party software from Microsoft that does the task more professionally, i do not remember the name.

    About reading two files at the same time, which is not exactly a simultaneous read action as was mentioned in previous posts, i think even if the read rate is not high, it's not a good idea to do this, specially if the hard drive is fragmented. because Drive Head should move between sectors so many times to read and buffer a file in one place and go back to read and buffer the remaining of the other file and so on. Since HDD life expectancy depends specifically on Drive Head moves, i think it will reduce the life span very much.
  11. Oct 12, 2011 #10
    Buffering the right thing at the right time can do wonders. That's part of the so-called "mystery".
    That's a technique you'll encounter EVERYWHERE in the business of processing data. For instance your DVD burn software probably buffers some amount of data from the slower access HDD to your RAM. Browsers buffer data from the slower internet medium to the faster local HDD. Your processor buffers data from the slow RAM(comparatively) to its own fast registers.

    And this piece of software you are referring to doesn't do it "more professionally", it just gives you more information and looks fancier that your average task manager.
    It is also called "Process Explorer" and is an incredible piece of software for monitoring just about everything your computer is doing in real time.
  12. Oct 12, 2011 #11


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    Sorry, this thread was originally posted almost two months ago. The technology has changed. All answers are no longer valid.
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