Physical hard drive failure.

Archived from groups: comp.sys.ibm.pc.hardware.storage (More info?)

I have a no-name (Platinum) 160GB 7200RPM hard drive that has had some
sort of physical failure. The bios sees it, but any reads from the
drive result in errors or time out. I have tried many hard drive tools
to try to recover the data, but all point to a physical failure. The
drive is not making the normal 'clicking' sound, but I can hear a
repetitive sound as if it's trying, and failing, to access the same
spot. In the past, I've always just RMA'd drives that had physical
failures if they were under warranty, or trashed them otherwise. This
time, I would like to try and see if I can fix the drive myself. The
data on there is not super important, but I would like to recover it if
possible. I'm willing to try anything to fix the drive, including
opening it, since it is no longer under warranty.

So, I guess my questions are:
1) Has anyone here ever fixed a drive with a physical problem?
2) Any guesses as to what component on the drive has most likely
failed?
3) Any websites detailing the steps to fix a physical hard drive
problem? (Google has been no help so far)
4) I know I could probably take this to some place and pay them
thousands of dollars to recover the data on it. So I'm wondering what
approach they take and if any of their techniques can be done at home
without expensive equipment.
5) Any other suggested groups to crosspost to?

Thanks.

--Phillip
17 answers Last reply
More about physical hard drive failure
  1. Archived from groups: comp.sys.ibm.pc.hardware.storage (More info?)

    Previously phillip.thurmond@gmail.com wrote:
    > I have a no-name (Platinum) 160GB 7200RPM hard drive that has had some
    > sort of physical failure. The bios sees it, but any reads from the
    > drive result in errors or time out. I have tried many hard drive tools
    > to try to recover the data, but all point to a physical failure. The
    > drive is not making the normal 'clicking' sound, but I can hear a
    > repetitive sound as if it's trying, and failing, to access the same
    > spot. In the past, I've always just RMA'd drives that had physical
    > failures if they were under warranty, or trashed them otherwise. This
    > time, I would like to try and see if I can fix the drive myself. The
    > data on there is not super important, but I would like to recover it if
    > possible. I'm willing to try anything to fix the drive, including
    > opening it, since it is no longer under warranty.

    > So, I guess my questions are:
    > 1) Has anyone here ever fixed a drive with a physical problem?
    > 2) Any guesses as to what component on the drive has most likely
    > failed?
    > 3) Any websites detailing the steps to fix a physical hard drive
    > problem? (Google has been no help so far)
    > 4) I know I could probably take this to some place and pay them
    > thousands of dollars to recover the data on it. So I'm wondering what
    > approach they take and if any of their techniques can be done at home
    > without expensive equipment.
    > 5) Any other suggested groups to crosspost to?

    Well, good luck. This is hi-tech you are trying to repair. In some
    (few) cases this might be feasible without much experience and
    without special tools, but in most cases you will not even be able
    to even diagnose the problem. You are trying something akin to brain
    surgery at home. True, the Azteks did brain surgery without
    modern medical knowledge or equipment and true, some of their
    patients survived, but care to guess how many did not?

    One word of advice though: As soon as you open the drive
    you have very limited time to repair and get the data off,
    unless you have access to a clean room. Depending on what
    particles settle on the disk's surface you may also have
    no time at all.

    Arno
  2. Archived from groups: comp.sys.ibm.pc.hardware.storage (More info?)

    phillip.thurmond@gmail.com wrote

    > I have a no-name (Platinum)

    Not clear what you mean by that. The name should show
    up on the black bios screen at boot time, and with Everest.
    http://www.lavalys.com/products/overview.php?pid=1&lang=en

    > 160GB 7200RPM hard drive that has had some sort of physical failure.

    Yeah, looks like it.

    > The bios sees it, but any reads from the drive result in
    > errors or time out. I have tried many hard drive tools to
    > try to recover the data, but all point to a physical failure.

    > The drive is not making the normal 'clicking' sound, but I can hear
    > repetitive sound as if it's trying, and failing, to access the same spot.

    Not all drive click when they recalibrate.

    > In the past, I've always just RMA'd drives that had physical
    > failures if they were under warranty, or trashed them otherwise.
    > This time, I would like to try and see if I can fix the drive myself.

    Not very likely with a drive that recent.

    > The data on there is not super important, but I would like
    > to recover it if possible. I'm willing to try anything to fix the
    > drive, including opening it, since it is no longer under warranty.

    > So, I guess my questions are:
    > 1) Has anyone here ever fixed a drive with a physical problem?

    Yes, and there is a difference between good enough
    to get most of the the data back and fixed properly.

    > 2) Any guesses as to what component on the drive has most likely failed?

    The only thing its possible to say is that it doesnt appear to be
    able to read the data off the platters properly. That can be due
    to a number of failures, everything from the read amp inside the
    sealed enclosure failing to a poor joint in the connection to that,
    to something more basic on the logic card. Not possible to say
    which it is without doing stuff like looking at the signals from the
    heads with a CRO etc.

    > 3) Any websites detailing the steps to fix a physical
    > hard drive problem? (Google has been no help so far)

    There's a few around, but they're all mostly rather silly.

    You could try putting the drive in a plastic bag and putting it
    in the freezer for a few hours and then checking to see if you
    can see any data on the drive as quickly as possible before it
    warms up. And repeat the process until you get the data you need.

    That can work if the fault is a dry joint or a crack
    in the flexible connection to the heads etc.

    > 4) I know I could probably take this to some place and
    > pay them thousands of dollars to recover the data on it.
    > So I'm wondering what approach they take

    Everything from checking those basics with a CRO and
    fixing what is found to be wrong to opening the drive in
    a clean room and fixing a physical problem in there, to
    replacing the head amp etc in a clean room.

    > and if any of their techniques can be
    > done at home without expensive equipment.

    Only really the freezing technique.

    With older drives you can often just replace the logic
    card with one off another drive of the same model,
    but that isnt very likely to work with a drive that
    modern, even with two brand new fault free drives.

    > 5) Any other suggested groups to crosspost to?

    This is the best for those questions.
  3. Archived from groups: comp.sys.ibm.pc.hardware.storage (More info?)

    phillip.thurmond@gmail.com wrote:

    > I have a no-name (Platinum) 160GB 7200RPM hard drive that has had some
    > sort of physical failure. The bios sees it, but any reads from the
    > drive result in errors or time out. I have tried many hard drive tools
    > to try to recover the data, but all point to a physical failure. The
    > drive is not making the normal 'clicking' sound, but I can hear a
    > repetitive sound as if it's trying, and failing, to access the same
    > spot.

    That's recalibration--it's either dealing with a marginal sector that is not
    quite to the point of being marked bad or something has gone wrong in the
    read circuitry so that all attempts at reads give the appearance to the
    firmware of being reads of bad sectors.

    > In the past, I've always just RMA'd drives that had physical
    > failures if they were under warranty, or trashed them otherwise. This
    > time, I would like to try and see if I can fix the drive myself. The
    > data on there is not super important, but I would like to recover it if
    > possible. I'm willing to try anything to fix the drive, including
    > opening it, since it is no longer under warranty.
    >
    > So, I guess my questions are:
    > 1) Has anyone here ever fixed a drive with a physical problem?

    It's been done.

    > 2) Any guesses as to what component on the drive has most likely
    > failed?

    The platter is most likely. If so you don't have a prayer of fixing it--the
    only possible repair is to read everything _else_ off of it, and if the
    sector the drive is trying to read is one that the drive needs in order to
    start then you're going to have to rewrite the firmware to not need that
    sector, which is for an individual whose understanding of disks is such
    that he has to ask questions here going to be a huge undertaking.

    It _may_ be that you have lucked out and it's an electronics problem, in
    which case replacing the circuit board with one from an identical drive
    might fix the problem.

    > 3) Any websites detailing the steps to fix a physical hard drive
    > problem? (Google has been no help so far)

    Not really.

    > 4) I know I could probably take this to some place and pay them
    > thousands of dollars to recover the data on it. So I'm wondering what
    > approach they take and if any of their techniques can be done at home
    > without expensive equipment.

    The only thing you can try that's not going to be expensive would be to swap
    out the controller, and don't bet on that working.

    Note that some of the recovery services now have reasonably low cost
    recovery available if you're willing to sit at the bottom of the priority
    queue for however long it takes.

    > 5) Any other suggested groups to crosspost to?
    >
    > Thanks.
    >
    > --Phillip

    --
    --John
    to email, dial "usenet" and validate
    (was jclarke at eye bee em dot net)
  4. Archived from groups: comp.sys.ibm.pc.hardware.storage (More info?)

    "J. Clarke" <jclarke.usenet@snet.net.invalid> wrote in message news:dcip1t019fl@news3.newsguy.com
    > phillip.thurmond@gmail.com wrote:
    >
    > > I have a no-name (Platinum) 160GB 7200RPM hard drive that has had some
    > > sort of physical failure. The bios sees it, but any reads from the
    > > drive result in errors or time out. I have tried many hard drive tools
    > > to try to recover the data, but all point to a physical failure. The
    > > drive is not making the normal 'clicking' sound, but I can hear a
    > > repetitive sound as if it's trying, and failing, to access the same spot.
    >
    > That's recalibration--it's either dealing with a marginal sector that is not
    > quite to the point of being marked bad or something has gone wrong in the
    > read circuitry so that all attempts at reads give the appearance to the
    > firmware of being reads of bad sectors.
    >
    > > In the past, I've always just RMA'd drives that had physical
    > > failures if they were under warranty, or trashed them otherwise. This
    > > time, I would like to try and see if I can fix the drive myself. The
    > > data on there is not super important, but I would like to recover it if
    > > possible. I'm willing to try anything to fix the drive, including
    > > opening it, since it is no longer under warranty.
    > >
    > > So, I guess my questions are:
    > > 1) Has anyone here ever fixed a drive with a physical problem?
    >
    > It's been done.
    >
    > > 2) Any guesses as to what component on the drive has most likely failed?
    >
    > The platter is most likely. If so you don't have a prayer of fixing it--the
    > only possible repair is to read everything _else_ off of it,

    > and if the sector the drive is trying to read is one that the drive needs in
    > order to start

    It's recognized by BIOS so obviously it passed that point.

    > then you're going to have to rewrite the firmware to not need that sector,

    In this case, just overwriting it.

    > which is for an individual whose understanding of disks is such
    > that he has to ask questions here going to be a huge undertaking.
    >
    > It _may_ be that you have lucked out and it's an electronics problem, in
    > which case replacing the circuit board with one from an identical drive
    > might fix the problem.
    >
    > > 3) Any websites detailing the steps to fix a physical hard drive
    > > problem? (Google has been no help so far)
    >
    > Not really.

    No 'details' but real people to help guide:
    http://forums.actionfront.com/

    >
    > > 4) I know I could probably take this to some place and pay them
    > > thousands of dollars to recover the data on it. So I'm wondering what
    > > approach they take and if any of their techniques can be done at home
    > > without expensive equipment.
    >
    > The only thing you can try that's not going to be expensive would be to swap
    > out the controller, and don't bet on that working.
    >
    > Note that some of the recovery services now have reasonably low cost
    > recovery available if you're willing to sit at the bottom of the priority
    > queue for however long it takes.
    >
    > > 5) Any other suggested groups to crosspost to?
    > >
    > > Thanks.
    > >
    > > --Phillip
  5. Archived from groups: comp.sys.ibm.pc.hardware.storage (More info?)

    Generally data recovery companies replace the drive's board first, then
    the preamp board inside the HDA. If that doesn't help, they may check
    if a head needs to and can be replaced. The last step is taking the
    drive apart, putting each platter on a spin stand (like a turntable)
    and reading the analog data with a high performance head and converting
    the flux changes into user data with software. This can generally
    recover anything that's not physically erased or damaged but takes a
    lot of time.

    Your drive clearly has problems reading data since you hear it
    retrying, but you won't be able to do anything about it (except maybe
    trying various temperatures.) If it was easy data recovery wouldn't be
    so expensive. Don't waste your time. An open drive makes a nice paper
    weight or bookend.
  6. Archived from groups: comp.sys.ibm.pc.hardware.storage (More info?)

    "RPR" <rohbeck@yahoo.com> wrote in message news:1122931870.433597.66940@o13g2000cwo.googlegroups.com
    > Generally data recovery companies replace the drive's board first, then
    > the preamp board inside the HDA. If that doesn't help, they may check
    > if a head needs to and can be replaced. The last step is taking the
    > drive apart, putting each platter on a spin stand (like a turntable)
    > and reading the analog data with a high performance head and converting
    > the flux changes into user data with software. This can generally
    > recover anything that's not physically erased or damaged but takes a
    > lot of time.
    >
    > Your drive clearly has problems reading data since you hear it
    > retrying, but you won't be able to do anything about it

    What exactly did you not understand in "It's recognized by BIOS".

    > (except maybe trying various temperatures.)
    > If it was easy data recovery wouldn't be so expensive.
    > Don't waste your time. An open drive makes a nice paper
    > weight or bookend.
  7. Archived from groups: comp.sys.ibm.pc.hardware.storage (More info?)

    RPR wrote:
    > Generally data recovery companies replace the drive's board first, then
    > the preamp board inside the HDA. If that doesn't help, they may check
    > if a head needs to and can be replaced. The last step is taking the
    > drive apart, putting each platter on a spin stand (like a turntable)
    > and reading the analog data with a high performance head and converting
    > the flux changes into user data with software. This can generally
    > recover anything that's not physically erased or damaged but takes a
    > lot of time.

    The technology you described does not exist, no data recovery company
    or intelligence/law enforcement agency recovers data by reading analog
    data off platters on a spin stand.
  8. Archived from groups: comp.sys.ibm.pc.hardware.storage (More info?)

    lazinator wrote:

    >
    > RPR wrote:
    >> Generally data recovery companies replace the drive's board first, then
    >> the preamp board inside the HDA. If that doesn't help, they may check
    >> if a head needs to and can be replaced. The last step is taking the
    >> drive apart, putting each platter on a spin stand (like a turntable)
    >> and reading the analog data with a high performance head and converting
    >> the flux changes into user data with software. This can generally
    >> recover anything that's not physically erased or damaged but takes a
    >> lot of time.
    >
    > The technology you described does not exist, no data recovery company
    > or intelligence/law enforcement agency recovers data by reading analog
    > data off platters on a spin stand.

    And of course you are privy to the internal workings of every law
    enforcement and intelligence agency in the world.

    --
    --John
    to email, dial "usenet" and validate
    (was jclarke at eye bee em dot net)
  9. Archived from groups: comp.sys.ibm.pc.hardware.storage (More info?)

    Previously lazinator <laslo@actionfront.com> wrote:

    > RPR wrote:
    >> Generally data recovery companies replace the drive's board first, then
    >> the preamp board inside the HDA. If that doesn't help, they may check
    >> if a head needs to and can be replaced. The last step is taking the
    >> drive apart, putting each platter on a spin stand (like a turntable)
    >> and reading the analog data with a high performance head and converting
    >> the flux changes into user data with software. This can generally
    >> recover anything that's not physically erased or damaged but takes a
    >> lot of time.

    > The technology you described does not exist, no data recovery company
    > or intelligence/law enforcement agency recovers data by reading analog
    > data off platters on a spin stand.

    HDDs have long since switched to analog reading and decoding, so there
    is no advantage left in doing so. With classical digital decoding
    doing maximum likelyhood decoding would gain you some signal
    improvement (1.5dB better S/N ratio, if I remember my coding theory
    course correctly). Not anymore.

    Arno
  10. Archived from groups: comp.sys.ibm.pc.hardware.storage (More info?)

    Arno Wagner wrote:

    > Previously lazinator <laslo@actionfront.com> wrote:
    >
    >> RPR wrote:
    >>> Generally data recovery companies replace the drive's board first, then
    >>> the preamp board inside the HDA. If that doesn't help, they may check
    >>> if a head needs to and can be replaced. The last step is taking the
    >>> drive apart, putting each platter on a spin stand (like a turntable)
    >>> and reading the analog data with a high performance head and converting
    >>> the flux changes into user data with software. This can generally
    >>> recover anything that's not physically erased or damaged but takes a
    >>> lot of time.
    >
    >> The technology you described does not exist, no data recovery company
    >> or intelligence/law enforcement agency recovers data by reading analog
    >> data off platters on a spin stand.
    >
    > HDDs have long since switched to analog reading and decoding, so there
    > is no advantage left in doing so. With classical digital decoding
    > doing maximum likelyhood decoding would gain you some signal
    > improvement (1.5dB better S/N ratio, if I remember my coding theory
    > course correctly). Not anymore.

    ????? Disks have always used analog signalling for data storage. One
    frequency it's a one, the other it's a zero.
    >
    > Arno

    --
    --John
    to email, dial "usenet" and validate
    (was jclarke at eye bee em dot net)
  11. Archived from groups: comp.sys.ibm.pc.hardware.storage (More info?)

    "J. Clarke" <jclarke.usenet@snet.net.invalid> wrote in message news:dcudne0fl3@news3.newsguy.com...
    > Arno Wagner wrote:
    >
    > > Previously lazinator <laslo@actionfront.com> wrote:
    > >
    > >> RPR wrote:
    > >>> Generally data recovery companies replace the drive's board first, then
    > >>> the preamp board inside the HDA. If that doesn't help, they may check
    > >>> if a head needs to and can be replaced. The last step is taking the
    > >>> drive apart, putting each platter on a spin stand (like a turntable)
    > >>> and reading the analog data with a high performance head and converting
    > >>> the flux changes into user data with software. This can generally
    > >>> recover anything that's not physically erased or damaged but takes a
    > >>> lot of time.
    > >
    I've heard this before from others.

    > >> The technology you described does not exist, no data recovery company
    > >> or intelligence/law enforcement agency recovers data by reading analog
    > >> data off platters on a spin stand.
    > >
    How would you know?

    > > HDDs have long since switched to analog reading and decoding, so there
    > > is no advantage left in doing so. With classical digital decoding
    > > doing maximum likelyhood decoding would gain you some signal
    > > improvement (1.5dB better S/N ratio, if I remember my coding theory
    > > course correctly). Not anymore.
    >
    I assume you are talking about PRML.

    > ????? Disks have always used analog signalling for data storage. One
    > frequency it's a one, the other it's a zero.
    > >
    Long ago FM/MFM worked like that. RLL uses single flux changes.
  12. Archived from groups: comp.sys.ibm.pc.hardware.storage (More info?)

    Previously J. Clarke <jclarke.usenet@snet.net.invalid> wrote:
    > Arno Wagner wrote:

    >> Previously lazinator <laslo@actionfront.com> wrote:
    >>
    >>> RPR wrote:
    >>>> Generally data recovery companies replace the drive's board first, then
    >>>> the preamp board inside the HDA. If that doesn't help, they may check
    >>>> if a head needs to and can be replaced. The last step is taking the
    >>>> drive apart, putting each platter on a spin stand (like a turntable)
    >>>> and reading the analog data with a high performance head and converting
    >>>> the flux changes into user data with software. This can generally
    >>>> recover anything that's not physically erased or damaged but takes a
    >>>> lot of time.
    >>
    >>> The technology you described does not exist, no data recovery company
    >>> or intelligence/law enforcement agency recovers data by reading analog
    >>> data off platters on a spin stand.
    >>
    >> HDDs have long since switched to analog reading and decoding, so there
    >> is no advantage left in doing so. With classical digital decoding
    >> doing maximum likelyhood decoding would gain you some signal
    >> improvement (1.5dB better S/N ratio, if I remember my coding theory
    >> course correctly). Not anymore.

    > ????? Disks have always used analog signalling for data storage. One
    > frequency it's a one, the other it's a zero.

    As you said "one is 1 the other is 0". But that is classical (M)FM.
    Modern modulation is far more sophisticated and modern disks read
    values 0.0 ... 1.0 for the bits and then decode them into the
    real target data or do error correction of these "soft" bits.
    Classical disks read the bits directly as 0 or 1 and if that
    failed did error correction on the hard 0/1 values.

    Arno
  13. Archived from groups: comp.sys.ibm.pc.hardware.storage (More info?)

    Arno Wagner wrote:

    > Previously J. Clarke <jclarke.usenet@snet.net.invalid> wrote:
    >> Arno Wagner wrote:
    >
    >>> Previously lazinator <laslo@actionfront.com> wrote:
    >>>
    >>>> RPR wrote:
    >>>>> Generally data recovery companies replace the drive's board first,
    >>>>> then the preamp board inside the HDA. If that doesn't help, they may
    >>>>> check if a head needs to and can be replaced. The last step is taking
    >>>>> the drive apart, putting each platter on a spin stand (like a
    >>>>> turntable) and reading the analog data with a high performance head
    >>>>> and converting the flux changes into user data with software. This can
    >>>>> generally recover anything that's not physically erased or damaged but
    >>>>> takes a lot of time.
    >>>
    >>>> The technology you described does not exist, no data recovery company
    >>>> or intelligence/law enforcement agency recovers data by reading analog
    >>>> data off platters on a spin stand.
    >>>
    >>> HDDs have long since switched to analog reading and decoding, so there
    >>> is no advantage left in doing so. With classical digital decoding
    >>> doing maximum likelyhood decoding would gain you some signal
    >>> improvement (1.5dB better S/N ratio, if I remember my coding theory
    >>> course correctly). Not anymore.
    >
    >> ????? Disks have always used analog signalling for data storage. One
    >> frequency it's a one, the other it's a zero.
    >
    > As you said "one is 1 the other is 0". But that is classical (M)FM.
    > Modern modulation is far more sophisticated and modern disks read
    > values 0.0 ... 1.0 for the bits and then decode them into the
    > real target data or do error correction of these "soft" bits.
    > Classical disks read the bits directly as 0 or 1 and if that
    > failed did error correction on the hard 0/1 values.

    Can you guide me to more information on this?

    > Arno

    --
    --John
    to email, dial "usenet" and validate
    (was jclarke at eye bee em dot net)
  14. Archived from groups: comp.sys.ibm.pc.hardware.storage (More info?)

    "J. Clarke" <jclarke.usenet@snet.net.invalid> wrote in message news:dcvrdq0e4k@news1.newsguy.com...
    > Arno Wagner wrote:
    >
    > >> ????? Disks have always used analog signalling for data storage. One
    > >> frequency it's a one, the other it's a zero.
    > >
    > > As you said "one is 1 the other is 0". But that is classical (M)FM.
    > > Modern modulation is far more sophisticated and modern disks read
    > > values 0.0 ... 1.0 for the bits and then decode them into the
    > > real target data or do error correction of these "soft" bits.
    > > Classical disks read the bits directly as 0 or 1 and if that
    > > failed did error correction on the hard 0/1 values.
    >
    > Can you guide me to more information on this?
    >
    It is all explained at PCguide, including PRML: http://pcguide.com/ref/hdd/geom/data.htm
  15. Archived from groups: comp.sys.ibm.pc.hardware.storage (More info?)

    I didnt say that i'm privy to the internal workings of every LEA/intel
    agency in the world, but you are so confident in your statement that
    you must be privy to it. You must've seen this magic machine with your
    own eyes ?

    Somebody asked "How would you know". Well, i've been doing this for a
    while and i talked to enough people in various agencies to know what
    they can and cant do.
    Coincidentally John isnt completely wrong, we developed technology he
    was describing and right now it's in a late prototyping stage. It was
    first publicly demonstrated at the NASA MSST2004 storage show in Apr
    of last year. But again, currently it is not being used in production
    recoveries, and nobody has/uses anything like this.

    Somebody had questions on how drives work internally, i can write some
    stuff up on monday if there's still interest.
  16. Archived from groups: comp.sys.ibm.pc.hardware.storage (More info?)

    Previously J. Clarke <jclarke.usenet@snet.net.invalid> wrote:
    > Arno Wagner wrote:

    >> Previously J. Clarke <jclarke.usenet@snet.net.invalid> wrote:
    >>> Arno Wagner wrote:
    >>
    >>>> Previously lazinator <laslo@actionfront.com> wrote:
    >>>>
    >>>>> RPR wrote:
    >>>>>> Generally data recovery companies replace the drive's board first,
    >>>>>> then the preamp board inside the HDA. If that doesn't help, they may
    >>>>>> check if a head needs to and can be replaced. The last step is taking
    >>>>>> the drive apart, putting each platter on a spin stand (like a
    >>>>>> turntable) and reading the analog data with a high performance head
    >>>>>> and converting the flux changes into user data with software. This can
    >>>>>> generally recover anything that's not physically erased or damaged but
    >>>>>> takes a lot of time.
    >>>>
    >>>>> The technology you described does not exist, no data recovery company
    >>>>> or intelligence/law enforcement agency recovers data by reading analog
    >>>>> data off platters on a spin stand.
    >>>>
    >>>> HDDs have long since switched to analog reading and decoding, so there
    >>>> is no advantage left in doing so. With classical digital decoding
    >>>> doing maximum likelyhood decoding would gain you some signal
    >>>> improvement (1.5dB better S/N ratio, if I remember my coding theory
    >>>> course correctly). Not anymore.
    >>
    >>> ????? Disks have always used analog signalling for data storage. One
    >>> frequency it's a one, the other it's a zero.
    >>
    >> As you said "one is 1 the other is 0". But that is classical (M)FM.
    >> Modern modulation is far more sophisticated and modern disks read
    >> values 0.0 ... 1.0 for the bits and then decode them into the
    >> real target data or do error correction of these "soft" bits.
    >> Classical disks read the bits directly as 0 or 1 and if that
    >> failed did error correction on the hard 0/1 values.

    > Can you guide me to more information on this?

    It has been a long time since I studied the subject. Google
    returns relevant hits for google(soft decision decoding) and
    google(maximum likelihood decoding). The actual decoding is
    significantly more difficult than the classical "hard" decoding
    and may even be prohibitively expensive for some codes.

    Unfortunately I did not find a concise introduction. The course
    I learned this had hand-drawn slides by the lecturer....

    Arno
  17. Archived from groups: comp.sys.ibm.pc.hardware.storage (More info?)

    I know we did it many years ago at DEC for customers who lost data on
    our drives. Combing in a new head stack was risky because the platters
    sometimes got scratched, so they took the disk stack apart. Generally
    we used a hand made souped up read channel with a spin stand, but I
    know of one guy who worked on A/D sampling the read signal from the
    preamp and storing one track worth of data in a high speed buffer that
    was interfaced to a VS4000. A few years back I chatted with a guy from
    Ontrack about this and he agreed that that's the way to go. If it's
    been used with high density disks recently I don't know. The main
    advantage I can see is that you don't have to rely on servo info which
    may be shot, or invalid if the platters have slipped. At each diameter
    you can decode a couple of sectors even if you don't compensate for
    runout. If you move the head in small enough increments (using e.g. an
    interferometer as the reference), you should be able to catch
    everything, a little in the way VXA does the reading. And I can easily
    imagine storing an entire analog image of the surface and running image
    processing algorithms on it. Hmm, TB sized images. Sounds like fun.

    Ralf-Peter
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