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Computer Hard Drives
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#1 Posted : Sunday, November 20, 2011 11:54:43 AM(UTC)
Admin Happy Ankle

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Computer Hard Drives


There are many very good articles on the Internet explaining how computer hard drive works, so we never wanted to write a similar article, telling the same basics. What we really want to talk about is Computer Hard Drive Bad Sectors.

A simple query like hard drive bad sector remapping to Google returns many really interesting things, that a good computer user needs to know. For example, you can easily find an article about hard drive bad sectors on Wikipedia, or the information about US Patent 5166936 called Automatic hard disk bad sector remapping, or the article called Bad Sector Blues. The last one is dated with 2006, and it tells about IDE hard drives, but it's still very good, because it explains the basic things about physical and logical structure of the hard drives. So we'd recommend you to make a quick search on the Internet and read about hard drive basics to understand the next few paragraphs.

Do people really understand the basics of computer hard drive? This is a very good question, because at least not so many people read all that stuff, preferring to ask same naive questions again and again, like "How do I repair bad sectors on an XP hard drive", or "how can I reformat my hard drive at the low level", etc.?

Short historical review

If we return back in the computer history we can find many exotic things about hard drives, how they appeared, their sizes, capacities, speed, power consumption, etc. Take a look at the article, telling about the First computer with the hard drive in the world, created in 1956. Below is the picture taken from this article, posted here just in case if this web site becomes inaccessible.

First computer with the hard drive in the world, 1956

Below is one more picture of this hard drive taken from We copied this picture for the same reason to prevent its loss if for some reason you can't find it there.

First Computer Hard Drive

We can probably find information about a very first computer virus written for a hard drive, moving the hard drive heads far away from the landing zone so badly, that they could be returned back only at factory using special tools. We can find articles about MFM drives, etc. We can find information about hard drive low level formatting, where we could set the hard drive sector interleave in a very wide range to significantly increase, or instead decrease the hard drive speed. We know about one such a case when the hard drive speed was increased in 4.5 times after such a simple change. But it was the epoch of the XT hard drives. All this stuff is too old, and the current computer generation of specialists never even heard about that.

Later, after IDE drives appeared, people kept talking about low level formatting. And there were many accidents, when computer hard drives died after occasional or intentional low level formatting made with the computer BIOS program. Many fatal accidents were related to Kalok Hard Drives. Only a few years later the reference to this function was removed from the BIOS of the most of computer brands. But even after that it was possible to call it, using a simple command line debugger, if we knew the exact address of this procedure in BIOS.

Approximately at the same time the hard drive developers blocked that hole in the hard drive firmware so that even if the user was thinking that he was making a low level formatting, it was just a high level formatting, nothing else. Beginning from that moment it became safe for the hard drives. They learned to emulate the low level formatting, actually ignoring these commands.

But why it was so dangerous? Describing that in simple words, the low level formatting was deleting the special marks on the hard drive surfaces, made at the factory, making the head positioning impossible. As soon as this info is deleted, the hard drive can never be recognized, initialized and calibrated to start working. End.

There were a few companies regularly publishing their own tools for low level and high level formatting of their hard drives. Except the formatting, that's what they all were made for, these tools were able to do many interesting things to the hard drives, for example, to localize bad sectors, to remap them, to show the bad sector table, to switch the hard drive mode, etc. But later even these tools mostly disappeared, and were replaced with light weight utilities to simply format the hard drives to start using them with some operating system.

Finally the low level formatting became obsolete, useless for a home user. If somebody still uses these words, he doesn’t understand the difference and the purpose of both formats. There are still many questions on the Internet like this: “Should I format my hard drive before installing Windows 7 on it?” and the answers from the “experts” like this: “If you've never done a low-level (full) format of the specific drive before, however, I'd personally do it before installing Windows 7. It will usually take a good amount of time, so I'd plan accordingly.” Period.

Current situation

The current situation is well described in many articles. The Wikipedia article about Bad Sectors tells that "A modern hard drive comes with many spare sectors". When a sector is found to be bad by the firmware of a disk controller, the disk controller remaps the logical sector to a different physical sector. In the normal operation of a hard drive, the detection and remapping of bad sectors should take place in a manner transparent to the rest of the system.” This is absolutely true. There is no hard drive without bad sectors. Even more, the hard drive surfaces usually degrade during work for many reasons:

  1. Computer was dropped.
  2. The hard drive heads scratched the surface because somebody pushed this computer while it was working.
  3. Something heavy was dropped on the table with the computer on it.
  4. Small piece of magnetic material from another location got between the flying head and the magnetic surface leaving a long scratch.
  5. Oil from the hard drive bearing flew away and then consolidated on the hard drive surface gluing the heads or at least decreasing the sensitivity of the heads just because the hard drive was overheated for different reasons like insufficient air flow around it, stopped cooler fan, etc., and finally the lubricant was defective. That was a reason of one serious recall of nearly 300,000 hard drives by one company developer a long time ago.
  6. Bugs in the hard drive firmware causing physical damages to the heads, etc. That particular case was a reason of hundreds of thousands of hard drive failures many years ago. We don't want to expose the company name here for obvious reason.
  7. Magnetic fields – somebody left his very good headphones near computer, or right on the top of his favorite laptop, and these headphones had 2 extremely powerful magnets to produce a very good music, like Sony MDR-V700). Depending on the power of the magnets and the distance, the user can lose the whole hard drive in just a few minutes to maximum in a few days. We know about two proven issues when 2-3 days were enough to get a permanent problem with the whole hard drive and the information on it. The reason - these headphones left by the copmputer case. The nearest hard drive died first. The second in the stack died a day later. Then these headphones were noticed and removed away.
  8. Bad mechanics of a particular hard drive, bad assembling line, etc. We'll discuss that later in this article.
  9. Bad cables, connectors, bad controllers, bad power supply, insufficient power, lower current than required, high temperature, glued or sealed hole in the hard drive case, etc.
  10. Multiple of Start-Stop cycles of a particular hard drive.

There are just a few examples here, and the real list can be much longer.

Start-stop vs. 24/7

This is not a question for computer professionals. According to the old statistics one start/stop cycle is equal to approximately 10 hours of a hard drive work. That includes only the 4500-5400 rpm hard drives. We don’t want to talk about hard drives with 4200 rpm, but there are much faster hard drives with 7200 rpm, 10,000 rpm and even higher. What about them? Can we assume that one start-stop equals to 15-20 hours of continuous work of this hard drive?

There are many articles on the Internet telling different versions about hard drive start-stop cycles. But should we really believe to all that? Our own personal experience shows that we need to be extremely careful with this info and don’t completely trust it. Today all the computers have a very nice, from the first view, feature to stop the hard drive when it’s not required. It lets the user save some time when he works with a battery powered laptop, or couple pennies for the entire year. But what is the real power consumption of a single hard drive comparing to a single AC unit in Arizona? It's less than negligible. For desktop it’s more a downside because each time when you need to read/write something, the hard drive should start spinning, then it should be initialized, calibrated, find the required track, etc. It takes several seconds and in most cases it’s very annoying. But this is only a visible part of the problem. Every start/stop operation decreases the hard drive life time. Even if we use a laptop with its small hard drive, the real life of the hard drive, working in this so called “green mode”, will be 6-12 months or maybe little longer longer depending on the number of these start-stops. Then the user will start noticing the bad sectors, etc. If we know and can disable this “feature”, then it’s fine. We can significantly extend the hard drive life cycle. One AZ company, having a lot of computers, making computer hardware for medicine, told us that their "laptop hard drives are pretty bad and die in approximately 6 or so months". When we asked if the green mode is enabled or not we got the answer, that they never even thought about that. After disabling this feature the whole situation changed.

There are some cases when the user cannot do anything to disable this feature. For example, you can buy a 1 TB or more “My Book” USB external drive. First, these models are mostly using a fast 10,000 rpm hard drive, providing a better speed and... higher heat. Second, these “My Books” don’t have any cooler fan inside, only the holes. The ventilation of these enclosures is only passive. As a result, these boxes should not be used continuously, they will simply overheat. Third, to compensate that, WD decided to stop these hard drives in 2-2.5 minutes after the last read-write operation. As a result, this 10,000 rpm hard drive has to start and stop every few minutes. We spent several hours testing My Book and got an unpleasant surprise with the Green Mode. We contacted WD support to ask if this feature can be disabled, and we got the answer that it can never be disabled, it’s in the firmware, etc. So the user has no access to this very important “feature” shortening the life of his computer hardware. With no doubt this “My Book” was returned back to the store, and we didn’t regret about that. Instead, it’s much better to buy an empty hard drive enclosure and install a hard drive that we need. It saves money in just a few minutes, because installing hard drive usually takes about 1, maybe 2 minutes, but never longer. And for sure this operation can’t worth $30-$50 or higher – the difference between the prices that we’d pay for these parts, getting the brand, that we really like, against the whole “My Book” in one piece. Plus the unstoppable Green Mode.

Deeper understanding of visible Hard Drive Bad Sectors

So we finally came to a very important paragraph. We know now that all the hard drives have bad sectors, but they are remapped, hidden both to operating system and user. Physically, the hard drive controller substitutes the location of a bad sector with a good one from a spare area of the hard drive. This is a normal operation. But here is a first point to stop at. It is extremely important to know where this particular hard drive was made, what country, what line, what was the condition of this line, etc. Many years ago there was a hard drive brand called Quantum Fireball. One Russian guy found a very interesting information about these hard drive controllers at the Quantum web site, and he wrote a small tool called QTest.exe to retrieve this info. Many years ago we used this tool to test several different hard drives. We had several pairs of hard drives made in different countries and then imported. It was the same brand and model, same year +/- a few months, same capacity, they were looking absolutely same excluding just one word following after Made in... The tests showed us a very important info. We don’t want to reveal the info about country origin of these hard drives in this web article, although we remember that and can recall if required. So, let’s use the numbers instead. After we tested these hard drives we got the following results.

  1. Box 1 – 0.04% and 0.024% of the spare space was used at the factory for the bad sector remapping.
  2. Box 2 – 0.17% and 0.14%.
  3. Box 3 – 4.2% and 8.4%.
  4. Box 4 – 14.2 and 17.4%.
  5. Box 5 – 38% and 42%.

We tested the same brand and the same model, but imported from different countries. The test results of the hard drives made in different countries were absolutely incredible! The difference was really huge! Even during the tests these hard drives were producing different noise.

It’s not a question what hard drive from the whole batch was the best. But in addition to these bad sector maps there were more points to pay attention at. The quality of the whole assembly was much better in the first case (number 1). These hard drives were able to position the heads much better, faster, more precisely, with lower noise, and the whole reading speed was significantly higher, especially comparing to the drives from the Box 5. The number of bad sectors also affected the reading/writing speed because instead of reading/writing the whole cylinder in one try (one or more spins depending on the controller and computer speed, reading mode, current drive mode, hard drive sector interleave, etc.) the hard drive had to change the cylinder moving the heads to the spare area and work with the good sector losing time for positioning, losing extra spin to get the required sector under the head, etc. But also keep in mind, that none of these hard drives showed any bad sector after formatting. But we can see now that the whole picture is way more complicated and not so many people have idea about these details.

Ok, these were brand new hard drives with just a few minutes to first hours of life experience, they didn’t get any consumer remapped bad sectors. But what should happen when the sector dies, becomes unreadable? It should be remapped, replaced with a good one… until the spare space is completely occupied.

Couple words about tests. Since we know now about bad sectors we also need to know how to understand which hard drive is good and which is not and will die pretty soon. There were always special tools known for prefessionals. One of them was VVSeek. It was simply showing the reading speed of the hard drive, cylinder by cylinder in graphical form. Having this diagram it was very easy to understand if this drive has remapped sectors and even estimate how many. How these results can be interpreted and understood is a special theme for another article. There are many other tests that one can find on the Internet. One of the good freeware tool is HDTune

Test of the hard drive with HDTune

It not only shows the speed diagram, but it can also retrieve the Hard Drive SMART info telling in detail for how long time this hard drive was used, how many start-stop operations it survived, seek/read errors, overheating, etc. There is a special documentation that everybody can find about this tool and how to read the results of the tests. There are just a coupe points we'd like to stop at. First, although this tool shows almost the same as VVSeek many years ago, these results cannot be used in the same way. The picture above shows a regular hard drive installed as a second one in the system. The primary hard drive has a different picture because the system reads its files, writes to the swap file, gets access to the files that it needs, there are many background processes running simultaneously and affecting the graph. Instead, when we were using VVSeek in MS DOS with no resident programs, no disk cache, etc., the picture was ideal. So the picture above cannot be used for a detailed analysis. Below is another screen shot of the test made against the same hard drive running as a system hard drive. There are multiple places on the test when the system simply interrupted the test and did something seriously affecting the results of the test. If we run the same test against the same drive one more time we'll get a similar curve but with different gaps. So, the best way to get the number of bad sectors is to get the SMART info from the hard drive. But here is the trap - this tool cannot get this info from the USB drive, or if the system uses the RAID ready drivers, etc. There are many limits that we cannot avoid directly. Professionals know about that and can do that, but that is at least a different and much longer article which is not yet even written. And who wants to share his professional tricks for free losing his time and typing that for the Internet? Good question.

Another hard drive test with HDTune

We could spend more time explaining how Zone Bit Recording works, what that is exactly, how it looks like at different test diagrams, and how can we read them. Or we could talk about the correlation between cluster size and hard drive file r/w speed. There are many things to talk about, and these themes are endless. But hopefully we covered one very important thing with this page - Bad Sectors.

The conclusion is pretty simple.


  1. If we can see the bad sectors on the hard drive then it is a very bad sign that the spare space is probably already occupied, and the firmware can’t remap the bad sectors to the hidden area. That means that beginning from this moment none of the bad sectors can be remapped. In other words, the situation is much more serious that most of the people think. The reasons? Read above.
  2. The quality of the hard drives, as well as other parts, dramatically depends on the country origin of these parts. The worse assembly quality leads to a sooner death of the whole hard drive because the mechanical problems cause more significant wearing out of the moving parts. it's like a snowball falling down the mountain - as lower as bigger.
  3. Start-stop feature, silently enabled by Microsoft after the next update that was installed, or intentionally enabled by user, will significantly decrease the life time of the hard drive, despite of the articles telling that the hard drives should always work this way. The most of the hard drive failures happen during start, keep that in mind.
  4. Although the current hard drives are much more robust and can survive the strong shocks, we’d never make these experiments with our own hard drives. Yes, we see in the documents that this particular hard drive, for example, will survive after a 10g shock working and 100g stopped. These numbers can be much higher. Do you still want to test that out? There are many factors affecting this assumption and we don’t like to test it with our own hard drives. If you can avoid placing your computer on a shaking table, don't place it.
  5. The important information, that you keep on your computer hard drives, should be at least duplicated and stored at a safe location. The regular backups of the hard drives, including the operating system, are not somebody’s good manner or habit. It’s a must to keep your data safe. If you want to never lose your files, simply follow this advice.

Comments from the author. First time this article was published a few years ago at Then I decided to publish it on thia forum to let people read and discuss it and probably add more interesting points.

@Copyright DSh

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