How hard drives work

LincLinc OwnerDetroit Icrontian
edited August 2011 in Science & Tech
Wonder what goes on inside that silver box that keeps all your data? Learn how current hard drives operate, and how solid state devices operate differently.
Most people have thousands upon thousands of megaybytes of data on their computer, and indeed the hard drives we used today to store all that information have grown by astronomical amounts since the early days, but have you ever wondered just how a hard drive actually works?

Comments

  • primesuspectprimesuspect Beepin n' Boopin Detroit, MI Icrontian
    edited June 2007
    FANTASTIC article, Rob. Great work :)
  • Sledgehammer70Sledgehammer70 California Icrontian
    edited June 2007
    Sweet! a place to point people to who ask... "How do Hard Drives work?"

    Great read Thrax :)
  • CycloniteCyclonite Tampa, Florida Icrontian
    edited June 2007
    Great work!
  • WingaWinga Mr South Africa Icrontian
    edited June 2007
    Great job Thrax. Even I understood it :D
  • osaddictosaddict London, UK
    edited June 2007
    That was cool thanks - a brief summary but still with depth! :D
  • docchrisdocchris
    edited June 2007
    From the section about the spindle motor:

    "Higher rotational velocities can significantly increase data read and write time"

    Surely it either increases read/write SPEED, or DECREASES the time taken
  • ThraxThrax 🐌 Austin, TX Icrontian
    edited June 2007
    Yes, that's correct. Thank you for pointing out the error. :) It has been corrected.
  • rice-burnerrice-burner
    edited June 2007
    Thanks for the hard drive technical review.

    I have a question regarding spindle speed vs areal density.

    Is it true that the maximum data rate read from the platter to the buffer (and visa versa) by a single read head, is proportional to SPINDLE SPEED x LINEAR TRACK DENSITY.

    So potentially the figure of performance for a disk drive is SPINDLE SPEED x SQUARE ROOT(AREAL DENSITY).

    In another words: A disk with twice the spindle speed is twice as good as the same disk with double the areal density instead.


    COOL.
  • ThraxThrax 🐌 Austin, TX Icrontian
    edited June 2007
    It is true, however as the spindle RPMs increase, the track density must decrease due to reliability concerns.
  • rice-burnerrice-burner
    edited June 2007
    Rice Burner said:

    So potentially the figure of performance for a disk drive is SPINDLE SPEED x SQUARE ROOT(AREAL DENSITY).

    Now ... Correcting my Math in conclusion ... Doh:

    In another words: A disk with twice the spindle speed should be equivalent in performance to the same disk with four times the areal density instead.

    Thrax replied:

    It is true, however as the spindle RPMs increase, the track density must decrease due to reliability concerns.

    Now thats straight. Thanks.
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  • MedlockMedlock Miramar, Florida Member
    edited June 2007
    A good read. Nice article, Thrax. :)
  • Naveed
    edited November 2008
    actually i have a harddisk whose actuator arms is continusoly moving to and fro. can any 1 resolve this probelm my e-mail id is munaveed2002@yahoo.com
    thanks
  • Confused
    edited January 2009
    What happens if the hard drive has more than one platter? Is data written to one platter then the next when the previous is filled. Or is the data spit up and written to all the platters at the same time making it faster than single platter disks.
  • ThraxThrax 🐌 Austin, TX Icrontian
    edited January 2009
    Hi, Confused. :)

    Hard drives put data wherever there's a physical space on any of the platters that's large enough to hold the binary in question. Once the data is broken down into small chunks called blocks, the file system (like FAT32 or NTFS) records where those blocks have been placed, and should they get shuffled around, where they have gone.

    It's easiest to imagine that a hard drive is a big filing cabinet with a master index on the side that lists where every page of every document is stored. A hard drive might not put all the pages in the same drawer, but instead you can read the index and see what drawer each page is saved in.

    A hard drive will attempt to store the entirety of a file on a single platter (it's faster this way), but it won't hesitate to store it on multiple platters if the need arises. As far as I am aware, a hard drive can only read from one armature at a time, though I'd be happy to see if I could get you an official answer from a hard drive manufacturer.

    The biggest speed boost for a mechanical drive comes from increasing the drive's areal density, or how many bits of data can be stored per square inch. The higher the density, the less distance an armature has to cover to load an entire file.
  • Davey Jay
    edited May 2009
    Thanks, this helped quite a lot when I had to reverse engineer one of these meanies (meanies because it cut me pretty well when I was fighting it open - rushed for time, had to get physical). Thanks!
  • cheer
    edited August 2011
    cheers for this, helped me lots with my ICT asignment :)
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