Defect Detection
(Magnetic Storage Rocket Science)
Magneto ... WHAT?

Earth to Gibson. Yeah, well, this is the kind of stuff that really gets Steve all excited (go figure.) So he thought (don't blame us) you might be interested in really knowing about the insane depth of technology built into SpinRite. Frankly, we doubt whether anyone but Steve and a handful of aliens would even know what all this is, but he's the boss, so here we go ........

Searching for "Weak Bits"

Since magnetic mass storage devices are not defect free, the best aid for the long-term maintenance of reliable data storage is the early detection and elimination of inevitable surface defects. These defects, which are caused by microscopic surface abrasions, scratches, pits, or any sort of uneven magnetic material plating, reduce the strength of the recorded signal when it is being read back. And as we saw on the previous page, defects also develop or “grow” due to a gradual evolution of the drive's storage surfaces through physical and magnetic stresses.

Therefore, the highest possible storage reliability can only be achieved by immediately removing, and never again using, any data from storage locations which are shown to have weakened data recording integrity.

The strategy used by SpinRite to detect
defective regions is unique in the industry:

SpinRite is actually able to lower the amplification of the drive's internal read-amplifier, then to cause the drive to encounter a "minimum amplitude" data signal. If that data signal happened to fall upon a spot of the drive's recording surface that is in any way "weak" then the drive will mis-read the data bit and return an error for the sector containing the bad spot. This signals SpinRite and the drive itself, that data should never again be stored within this region.

Now, how in the world can a software utility program "turn down" the amplification gain in the drive's read amplifier, then deliberately cause the drive to attempt to read a weak data signal?

The SpinRite Defect Detection Invention

The read amplifiers of all magnetic storage devices contain an automatic gain control (AGC) that dynamically adjusts the amplifier's gain to the strength of the signals being received from the drive's head. This compensates for physical variations such as the head's flying height and media plating thickness. The AGC circuitry raises the amplifier's gain in response to low-amplitude data and lowers the gain when high-amplitude pulses are being received.

SpinRite cleverly uses this fact as follows:

As you can see in the diagram and description above, by deliberately alternating large and small data pulses, SpinRite keeps the drive expecting large pulses, but then it "sneaks in" the smallest pulses possible while the drive's read amplifier gain is still turned way down from the large pulse that precedes each small pulse.

This system works incredibly well. But since only those small surface regions beneath each small pulse are receiving the maximum test, a "family" of data patterns -- each shifted over by one pulse-period -- must be written and read in order to thoroughly test the entire surface of the drive.

The diagram to the left shows this "family" of pulses which completely scrubs the entire surface of any magnetic mass storage system, thoroughly testing each possible data storage bit position on the system's data recording surfaces.

This set of data being written and read by the drive is what we call a system of "worst case data patterns" because they deliberately create more trouble for the drive's data reading system than any "normal" data that any user would typically store. But this fact, the existence of something like "worst case data patterns" also demonstrates something which isn't generally understood:

The PARTICULAR DATA being written
and read from the drive MATTERS!

This is significant when SpinRite is compared with ANY other utility, since ONLY SPINRITE tests magnetic data storage surfaces with data patterns. All other utilities, like Scandisk, simply read whatever data happens to be on the disk at the moment ... which tells you and the drive nothing about the actual condition of the data storage surfaces beneath the data.

And that is important because when your data is written onto the disk, it might happen to generate a small pulse over a weak spot ... and be unable to be read back by the drive! You'd rather find out about that while your data is safe and you're running SpinRite, than when you're trying to read your own data!

You still want to know more?
There IS more!

You have probably been asking yourself ... "So exactly how does SpinRite deliberately generate large and small pulses on the recording surface?"

Ahhhhh, a good question!


As we've seen above, the key to accurate defect detection lies in deliberately generating a series of pulses of alternating size. This is done by taking advantage of the fact that data pulses occuring near one another interact with one another. Here's what we mean:

Data bits are recorded on a magnetic surface by reversing the direction of the magnetism at a location. This magnetic reversal event is later picked up when the drive is reading. This event is treated as a data bit from the drive. Since a reversal of the magnetic field means making it go in the opposite direction, the signal picked up when reading the disk alternates in polarity, with a positive pulse followed by a negative pulse, followed by a positive pulse, followed by a negative pulse, and so on ...

If the pulses were ideal, perfect and square, the result would look something like this:

Notice that the pulses alternate in direction and return to the center.

If the pulses being read back from a magnetic disk were really this perfect, then there would be nothing like "worst case patterns" since each and every pulse would stand on its own without interacting with its neighbors. But reality is much more messy. The diagram below on the left shows a single, perfect, idealized pulse like those above, and the diagram below on the right shows the actual shape of the pulse that is read back by a magnetic read head:

Ideal Pulse

Actual Pulse

As you can see, actual pulses are significantly rounded and are much broader. This pulse breadth creates data pattern sensitivity because closely spaced pulses of opposite polarity overlap each other and partially cancel each other out. SpinRite understands and exploits this characteristic by deliberately synthesizing pulses of differing amplitudes for surface pattern analysis. Here's how this works:

Typical Worst Case Pulse Sequence

In the diagram above, the first two pulses are spaced very far apart from all others so that they do not overlap and will be read as maximum amplitude pulses. This tricks the drive's read amplifier into turning down its amplification gain since it presumes a strong signal coming from the drive's read head. But unlike the first two pulses, the last three pulses are spaced as closely together as possible.

Look what happens when we change our view from "theoretical pulses" to "actual pulses" ...

Actual "Worst Case Pattern" Pulses Read Back From Disk

The big A and B pulses are read back with maximum amplitude because no other pulses are nearby. But the negative polarity D pulse, being tightly sandwiched in between the two positive polarity C and E pulses, gets pulled upward by its positive neighbors, so it isn't nearly as strong as it would normally be!

If there's ANYTHING at all weak with the magnetic storage location lying directly beneath the deliberately weakened D pulse, then that D pulse will read back even weaker, will be regarded as "noise" and won't be detected at all. THE SECTOR READ ERROR that results means that SpinRite will have succeeded in demonstrating to the drive that this area is no longer safe for storing the user's data, and that the drive should take this sector out of service and replace it with a spare.

ALL OF THE TECHNOLOGY that's described above is completely unique to SpinRite and does not exist in any other utility that's ever been created. As Stephen M. Leon wrote in his Microsystems Magazine review of SpinRite:

"SpinRite describes itself as a truly new generation of hard disk utilities, which is a marvel of understatement."

We have seen that mass storage systems need periodic preventive maintenance because surface defects actually GROW on magnetic storage surfaces. SpinRite makes this preventive maintenance easy and painless.

Doesn't it just make sense to store your data on drives that are periodically checked and surface-scrubbed with SpinRite?

The BEST News of ALL

The best news of all is that you don't need to understand any of this crazy space alien technology to get 100% the benefit from it all. SpinRite hides its technology behind a straightforward and simple to use interface that you basically just start up and leave alone for a few hours. That's really all there is to it!

Now you have a sense for the quality and quantity of SpinRite's unique technologies that run inside your computer system to take care of your drives whenever you use SpinRite.

SpinRite Overview Screen Shots Documentation
Defect Detection Data Recovery Reviews
Exclusive Features Feature Summary SpinRite Q&A
Version History Notify me of important news!

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Last Edit: Feb 22, 2008 at 09:39 (3,352.81 days ago)Viewed 5 times per day