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How to determise the physical location of a file on a CD ?

Discussion in 'Hardware' started by Doublehp, May 22, 2004.

  1. Doublehp

    Doublehp Guest

    I have to build an ISO with only two specs:
    - I have to know where is a given file, I mean, I have to know how far
    from the center of the CD is a particular file
    - the file has to be alone in that zone.

    I can choose what ever I want to do that: ISO, Joliet, or what ever.

    Since I expect a CD to have interlaced sectors like a HDD, I think
    that the easiest way is to declare two white 50M files, one before and
    one after, and build the raw image using the UNIX tool mkisofs.

    Then remain two questions :
    - how to know where will be located the given file (on which circle it
    will be burnt - how far from the center will it be )
    - how to make sure no file will overlap that zone (how to make sure
    only the two white files will be wixed in the same circles than the
    given file)

    Thanks for help.
    Doublehp, May 22, 2004
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  2. Doublehp

    Aaron Guest

    You could just use a simple ratio to do the job. For example, if you
    want the file half-way out from the middle, then you figure out the
    ratio of the area of a circle to the area of a circle with half that
    diameter. Then you will know how much "white file" to put on each
    side of your real file, and it should go in the correct place.

    Aaron, May 23, 2004
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  3. Doublehp

    Joe Wright Guest

    I'm assuming by 'circle' you mean 'track' and 'sector' some fraction
    of a track, a la HDD. CD's don't work like HDD's. There is one
    spiral track beginning near the spindle and ending near the outer
    perimeter of the disk. Do some more reading.
    Joe Wright, May 23, 2004
  4. Doublehp

    Aaron Guest

    Whoa, looks like you (doublehp) accidently cross posted. Here is your
    Well, I don't think that it is so complex. It should be fairly
    similar (in fact, derived from) the formula for the area of a circle:

    So, let's do an example: You want a track burned 1/3 out from the
    middle (measuring from where the data starts). Use a ruler, and find
    out how far from center of CD that is. Find the area using that
    radius, and then subtract the area of the middle of the CD (the
    "hole"). Thus, after subtracting the two, you have the "area" of data
    that you will need before your track. We will call this area1.

    Next you need to figure out the area of the data you need after your
    track. This is similar to the above. First, find out the total area
    of the disk, and then subtract from that the area of the "hole". Also
    subtract the area of the data before your track, and then you will
    have the second of your two numbers. We will call this area2.

    Now we want those in ratio. So put it like this area1:area2
    For 1/3, I guessing maybe...well, I don't know, and I don't have the
    correct tools here with me at school to try it out, so you're on your

    Anyway, with your ratio, just make two of your "white files" with
    proper lengths so as to fill the CD (that's important--CD must be
    filled for track to be in proper location), keeping in mind that they
    have to be in ratio also. That should about do it.

    Hope it's understandable,

    Aaron, May 24, 2004
  5. I think you are assuming bits per square inch is a constant. AFAIK CDs
    maintain a constant head velocity which means lineal bits/inch is a
    variable; a function of where the square inch is on the physical CD.
    kevin collins, May 24, 2004
  6. Doublehp

    Willem Guest

    kevin wrote:
    ) I think you are assuming bits per square inch is a constant. AFAIK CDs
    ) maintain a constant head velocity which means lineal bits/inch is a
    ) variable; a function of where the square inch is on the physical CD.

    CDs maintain a constant *linear* velocity which means that the number of
    bits/inch along the line *is* constant, and therefore the number of
    bits/sqare inch is also constant.

    You may be thinking of constant *angular* velocity.

    SaSW, Willem
    Disclaimer: I am in no way responsible for any of the statements
    made in the above text. For all I know I might be
    drugged or something..
    No I'm not paranoid. You all think I'm paranoid, don't you !
    Willem, May 24, 2004
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