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Thread: Seagate MFM drive model numbers and differences ?

  1. #11
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    Quote Originally Posted by Dwight Elvey View Post
    RLL drives have a little more band width than non-RLL otherwise the are the same.
    Dwight
    Wrong. RLL has not higher bandwith, the bits per inch resolution on a track is exactly the same. ALso the raw data transfer rate betwen the drive and the harddisc controller is the same. RLL is only a more effective encoding. RLL contains less of sync clock signal, but more data signal, that's all. But that needs a (bit) better magnetic surface quality. That's the difference.

  2. #12
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    Quote Originally Posted by 1ST1 View Post
    Wrong. RLL has not higher bandwith, the bits per inch resolution on a track is exactly the same. ALso the raw data transfer rate betwen the drive and the harddisc controller is the same. RLL is only a more effective encoding. RLL contains less of sync clock signal, but more data signal, that's all. But that needs a (bit) better magnetic surface quality. That's the difference.
    If we're going to split hairs here about the meaning of 'band width'.... The bits per inch resolution is higher with RLL (2,7), but the number of potential flux transitions per inch is the same as with MFM, aka RLL (1,3).

    You could say RLL (2,7) has a higher bit rate than MFM, but the same normalized baud rate.

    In the analog domain this could be represented, as stated by Dwight, as a greater 'band width;' while the highest frequency allowed may not increase, band-width is also increased when the lower frequency limit is extended downwards, even if the upper frequency is not increased. Magnetic recording imposes a high-pass filter; change the high-pass lower cutoff frequency down, and the band width increases, even if the low-pass filter at the upper cutoff doesn't change. See https://en.wikipedia.org/wiki/Run-length_limited

    The longer allowed run length effectively extends the lower frequency cutoff downwards; even though the upper frequency is still fixed at a certain rate (due to head gap size), the lower frequency limit being moved downwards gives a larger band width. It's very similar to the massive effective band width increase imposed on video tapes by the use of the luminance NBFM technique in conjunction with the interleaved color-under technique; a tape that could normally only record a bandwidth of 10 octaves, using NBFM an effective bandwidth of over 16 octaves can be successfully recorded and played back. The maximum upper frequency doesn't change; but the lowest effective frequency is lowered dramatically, well below 60Hz.

    NBFM, like RLL, is an encoding technique. It does require a good linear 6dB per octave rolloff on the low side, and thus better tape is required, much like better disk media is required to extend the effective bandwidth downwards using RLL encodings (use of both 2,7 and 1,7 is out there).
    Last edited by lowen; May 21st, 2020 at 11:55 AM.
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  3. #13
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    I saw another one today with "PR" following the model number sticker, same style as the "MLC" sticker. Interesting

  4. #14

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    Quote Originally Posted by 1ST1 View Post
    Wrong. RLL has not higher bandwith, the bits per inch resolution on a track is exactly the same. ALso the raw data transfer rate betwen the drive and the harddisc controller is the same. RLL is only a more effective encoding. RLL contains less of sync clock signal, but more data signal, that's all. But that needs a (bit) better magnetic surface quality. That's the difference.
    I believe that is what I said.
    Dwight

  5. #15

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    Quote Originally Posted by Dwight Elvey View Post
    I believe that is what I said.
    Dwight
    I should clarity. Smaller domains on the surface, improve bandwidth. It is not that the data frequency is changed but the timing accuracy of the edges are are improved. This is the same as improved bandwidth.
    This is just the same as on a cassette tape. Smaller domains mean it can have higher frequency information. Even if the frequency of the written data is the same it will have less jitter. This amounts to improve bandwidth.
    Dwight

  6. #16
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    I found the following interesting explanation of "PR" model code in the ST11R/ST11M manual:

    ---
    Paired Program drives are shipped with a Seagate controller. They
    are recognized by a "PR" label on the drive top cover. Paired
    drives are shipped formatted with a small DOS partition
    containing the installation program, INSTALLR, which will low-
    level format and partition your drive. You must supply the DOS
    program. The ST11M/ST11R can recognize whether a drive has the
    Paired Program software loaded, or has been previously installed.

    Paired Program drives with formatted capacities greater than 32
    MBytes have Disk Manager partitioning software loaded. This
    utility has been customized by Ontrack for Seagate. Refer to
    Section 2.1 for special instructions on formatting Paired Program
    drives.
    ---

  7. #17

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    One wonders about the "pairing". Might it be to automatically deal with known bad tracks? Most MFM controllers can easily reformat and partition disk drives. I guess for some people it is kind of intimidating. Getting such things already done and only requiring the OS install might be as much as the average person expected to deal with. Also, for people that will build 10 or more system a day for businesses, it might make sense. In such an environment, time is not free. Something I might fiddle with for a few hours is not something that makes sense in an IT environment. Getting it done quicker might make sense, even for someone that knows what they are doing.
    Dwight

  8. #18
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    Quote Originally Posted by chris_nh View Post
    I've also seen some part numbers like "ST-251 -1". Same curiosity... what does -1 specify?
    The ST-251-1 drivers were an improved variant of the standard 251 drives with faster transfer speeds and seek times. At least according to the Red Hill Guide.

    http://redhill.net.au/d/5.php

  9. #19

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    Quote Originally Posted by AndyM1981 View Post
    The ST-251-1 drivers were an improved variant of the standard 251 drives with faster transfer speeds and seek times. At least according to the Red Hill Guide.

    http://redhill.net.au/d/5.php
    Transfer speed is the same, just the seek times are improved.

  10. #20

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    Hi,

    I am not sure what you are specifically looking for. However, if you look at here:

    ftp://ftp.seagate.com/pub/techsuppt/

    you will find documentation for all seagate drives, incl. their specs. This might help you find out the differences you are looking for.

    Best Regards

    Jens

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