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Hard Drive questions

Discussion in 'A+' started by mikehende, May 25, 2006.

  1. mikehende

    mikehende Kilobyte Poster

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    MM says that
    "You're never going to have to deal with Data Encoding"

    but I don't understand anything concerning this, from "Flux reversal" to "timing bits" to "FM-Frequency Modulation" to "MFM-Modified Frequency Modulation" to "RLL" to "PRML". Can anyone PLEEEEEEEEASE explain this to me?
     
  2. Bluerinse
    Honorary Member

    Bluerinse Exabyte Poster

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    LOL Mike's thirst for knowledge knows no bounds :blink

    Okay, Frequency Modulation (FM).

    Basically you have a carrier frequency usually in the RF spectrum. Without modulation it would be a perfect sine wave. What modulation does, is to alter the frequency of the carrier wave in sympathy to another signal. In radio for example the carrier wave would be modulated by an audio wave. So the resultant modulated carrier wave is a combination of an RF signal and an audio signal.

    Of course you would need to de-modulate the modulated carrier wave in order to extract the original audio.

    It is similar to Amplitude Modulation (AM) except that AM has it's amplitude modulated rather than the carrier frequency.

    I have only made an effort to briefly answer one of your questions. The complexity of the subject matter that you are delving into far exceeds the requirements of the A+ and each one could most probably fill books on their own.
     
    Certifications: C&G Electronics - MCSA (W2K) MCSE (W2K)
  3. phoenix510

    phoenix510 Byte Poster

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    Thanks for asking that question Mike : as I have also just started that chapter in the MM book and my head just exploded trying to get to terms with the flux reversals and the rest of the jargon and thats after reading the areas twice :eek: . Thanks for the advice Bluerinse. :)
     
    Certifications: ECDL, MOS WORD & Excel, MCDST
    WIP: A+ & 70-270
  4. hbroomhall

    hbroomhall Petabyte Poster Gold Member

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    As MM says - most of the detail is way beyond A+ requirements.

    "Flux reversal" should be school physics. It is how a tape recorder works.

    Magnetize a bit of tape one way - then magnetize the next bit the other way. Now run this past something like a small compass. At the junction of these bits the compass will change position. School physics told you that a varying magnetic field will produce a current in a nearby wire. Amplify this and you get your recording from the tape.

    In the digital world we are only interested in 'on' or 'off'. So you *could* arrange that one direction of magnetization is '1' and the oposite is '0'. A '1' next to a '0' on a tape is a flux reversal - the magnetic flux has changed direction.

    The snag is that you can only detect *changes* in the magnetic field in your nearby wire. So a '1' next to another '1' produces no signal - nothing has changed. So you have to get a little tricky, and 'encode' your bits in a way that produces at least one change for each bit.

    Whole books could (and have) been written on this subject!

    Harry.
     
    Certifications: ECDL A+ Network+ i-Net+
    WIP: Server+
  5. mikehende

    mikehende Kilobyte Poster

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    Now we're getting somewhere so this leaves still to get simplified answers for "timing bits", MFM-Modified Frequency Modulation, RLL and PRML.
     
  6. hbroomhall

    hbroomhall Petabyte Poster Gold Member

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    There is a good article on this here .

    This appeared on the first page of a Google search on flux reversal. Google really is your friend! :biggrin

    Harry.
     
    Certifications: ECDL A+ Network+ i-Net+
    WIP: Server+
  7. mikehende

    mikehende Kilobyte Poster

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    Harry, no need for you or anyone else to remind me about using google, I "always" try BOTH google and yahoo before posting here, when I can't get something simplified enough for me then I post here, thanks for the link, will look into it in a few.
     
  8. mikehende

    mikehende Kilobyte Poster

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    Found and tried that link already, didn't do it for me, thanks anyway. What I am attempting to do is to get separate tutorials for each item listed above and try to put them together, for example, I will take your explanation of Flux Reversal and someone else's on RLL, then someone else's on MFM and so on, will post the final draft here.
     
  9. mikehende

    mikehende Kilobyte Poster

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    NOW I see why you guys are saying that this issue can take up an entire book, went to do more indepth research on MFM and came upon a great site for EVERYTHING regarding hard drives

    http://www.pcguide.com/ref/hdd/geom/dataMFM-c.html

    only problem is, this way too in-depth for my liking and will require a lot of time to understand all that's written there so I will take everyone's [and MM's] advice here and skip this. I will print this out and read this when in the car on a long drive when the wife is driving, this way, I will have a general idea of everything associated with the hard drive but don't have to memorize it. So now, on to the next step.
     
  10. Mr.Cheeks

    Mr.Cheeks 1st ever Gold Member! Gold Member

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    are you sure you can study when your having a long journey with the other half? you must be one of the lucky ones... :biggrin
     
  11. mikehende

    mikehende Kilobyte Poster

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    No, not "study", just read through it and like I said, not have to "memorize" it.
     
  12. Mr.Cheeks

    Mr.Cheeks 1st ever Gold Member! Gold Member

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    my apologises Mike...
     
  13. mikehende

    mikehende Kilobyte Poster

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    for what?
     
  14. hbroomhall

    hbroomhall Petabyte Poster Gold Member

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    Er - <cough> - that is the same piece that I mentioned!

    Harry.
     
    Certifications: ECDL A+ Network+ i-Net+
    WIP: Server+

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