This article will illustrate you what bad sector is and how to repair bad sector.

Bad sector is the place where you can’t write data. Almost all hard disks have bad sectors.


  1. When a file is read or a program is ran, hard disk is repeatedly read and has error prompting file corruption and other information; or it needs a long time to finish reading and sometimes there will even be a blue screen on computer.
  2. The sound of hard disk suddenly turns into strange sound from the original normal friction sound.
  3. System can’t start normally excluding the reason of virus infection. The prompt message of “Sector not found” or “General error in reading drive C” appears.
  4. When hard disk is formatted, operations interrupt at a certain schedule. And finally computer prompts error suggesting that operations can’t be finished.
  5. Scandisk will be automatically run to scan disk error each time when computer is started.
  6. When you perform FDISK on hard disk, the operations to a schedule will be repeatedly forward and backward.

2.Two Types

Soft Bad Sector

It is produced due to hard disk wear during formatting. You can mark them out or repair them by re-formatting. You must remember that if you format hard drive, the data will be completely lost.

You can use MiniTool Partition Wizard and its “Surface Test” function to check whether there are bad sectors on the hard disk. If there are, you can then search a way on the internet to repair these bad sectors.

Physical Damage

Physical damage can’t be repaired. Data will never be able to be written to this sector. If there is such a bad sector on hard disk, this hard disk is almost useless.

Hard disk is divided into memory cell in units of sectors for storing data. Each hard disk has tens of thousands of sectors. Before hard disk stores data, bad sectors are marked out to make computer don’t write data to these sectors. In order to avoid losses brought by bad sectors, you should test computer every six months. At the same time, you should avoid hitting or bumping hard disk. If there are some continuous bad sectors, this means that hard disk is badly worn. If the number of bad sector is increasing fast, you had better back up all data and closely monitor its work. This may be the time to replace the hard drive. Therefore, the best way to deal with bad sectors is to mark them out. You can achieve this by running scandisk.

3.Repairing Principle

(1) A part of bad sectors can be repaired by rewriting the checksum and other identifying information.

Now, hard disk manufactures offer some basic hard disk maintenance tools, such as the various versions of DM, POWERMAX and DLGDIAG. Such kinds of tools include the features of Zero fill or Low level format. When these two features are used, the data on the disk are cleared. And when you use these features, the checksum and identifying information of every sector will be rewritten. If hard disk surface medium isn’t damaged, most of the bad sectors can be corrected to a normal state. This is what called “logical bad sectors can be repaired”.

(2) Auto-repair mechanism is called to replace bad sectors.

In order to reduce repair times of hard disk, disk manufactures design the auto-repair mechanism, namely Automatic Reallocation or Automatic Reassign inside hard disk. All the current produced hard disks have such a function: during the process of reading and writing hard disk, if a bad sector is found, internal management program will automatically allocate a spare sector to replace this bad sector. Internal management program also records physical location and replacing details in G-list (Grown defects list).

As a result, a small number of bad sectors are automatically replaced during usage process. They don’t affect much on users’ normally use. There is also some hard disk auto-repair mechanism whose excitation conditions are strict. And some pieces of program, such as commonly used Zero fill in Low format DM, Wipeinfo in Norton, correction tools, wddiag in Western Digital Kit and Erase of DFT in IBM, are run to detect and judge bad sectors. They also issue appropriate instructions to stimulate auto-repair function.

There also exists some semi-professional tools like HDD speed, MHDD, HDDL, HDD utility and so on (you can search on the Internet to download). These tools are able to eliminate some bad sectors after running, mostly because they can stimulate auto-repair mechanism when detect bad sectors. If readers can see the G-list, they will know that G-list records may be increased to a certain amount before or after these repair tools run. For example, using HDD speed can view P-list and G-list of Quantum Fireball series; using MHDD can view P-list and G-list of IBM and FUJITSU.

Of course, G-list records are limited. G-list of all hard disk will be limited to a certain number range. For example, limitation number of Fireball series is 500; limitation number of Diamond II is 636; limitation number of Western Digital Kit BB is 508. The auto-repair mechanism can’t repair the bad sectors if records are over the limit number. This is why a small number of bad sectors can be repaired with the above tools while a large number of bad sectors can’t be repaired with these tools.

(3) Defective sector will be recorded in P-list and performed with internal low-level format by using professional software.

Hard disk can be accessed according to logical address mode rather than physical address mode when users use it. When hard disk proceeds self-test in power-on state, system will read some specific parameters (which are closely related to the parameters called during internal low-level format) from its reserved area and store them in buffer. These parameters are used as transition basis between physical address and logical address.

Some professional software will convert logical address of tested bad sectors to corresponding physical address and directly record this in P-list. Then, the software will call the internal low-level formatting program for low-level formatting. This can avoid the limit of G-list and repair lots of bad sectors.

4.Repairing Methods

If damage of hard disk belongs to logical corruption, we can re-install the software. What if it belongs to physical corruption? Actually, as long as damaged condition isn’t so serious, generally, the problem can be solved with some means.

Inspection before Repairing

At first, we should know the phenomena showing that hard disk has physical bad sectors.

  1. Errors often appear when system reads some file or runs some software; or a very long time is needed before operation is successfully completed. During the process, hard disk is repeatedly read and issues harsh noise. This phenomenon means that some sectors containing data on hard disk have been damaged.
  2. The system can’t boot by hard disk. Although you can see drive letter after system boots with floppy disk, the drive can’t be accessed. You even fail to use SYS command to conduct system. This condition is very serious, because it’s most likely that there is problem in the hard disk boot sector.
  3. A blue screen appears frequently for no reason when you normally use computer.

Specific Solutions

For the previous three circumstances, we generally have ways to make remedy. Here are several ways of repairing hard disk bad sectors. You should know that priority should be given to top ranking methods.

(1 ) Firstly, we should start with the easiest way. You can select hard disk drive letter from Win 98 Explorer first; secondly, you should right click on it and select “Properties” from the shortcut menu; thirdly, you can do full scan operation on hard disk in “Tools” and correct the possible bad cluster.

If Win 98 can’t be entered, you can use its boot disk to start. Then you may enter “scandisk X:” (X is a specific drive letter) behind the prompt “A: >” in order to scan the disk. For bad cluster, the program will mark it out by using read letter “B” (bad) with black base (Note: scandisk can’t detect and scan hard disk over 200G).

(2) In fact, the first method usually doesn’t work, because “bad sectors” auto-repair of Win 98 largely aims at logical bad sectors rather than physical bad sectors, so, we should consider to proceed “cold treatment” to these bad sectors. “cold treatment” means that we can mark the bad sectors and don’t use them. We should remember location of bad sectors in the first method and then do advanced formation to hard drive in order to put the areas with bad sectors into an area.

Later, we shouldn’t save files on this area. To illustrate, we should leave appropriate space rather than divide this area too “economically”, because it’s unwise to read the “good” ones around the bad ones – bad sectors can spread. If hard disk reads the “good” ones which are too close to the bad ones, then sooner or later, there will be new bad sectors on hard disk.

(3) You can manage hard disk with some software. Partition Magic is the most typical one. Here we just take version 5.0 as an example. “check” command in Partition Magic 5 can be directly used to scan hard disk, but this command have no auto-repair function. Therefore, we had better call relevant programs of Win 98 in Partition Magic 5 to complete the auto- repair task. After bad cluster is marked, we can try re-testing it.

The method is to choose “Advanced/bad Sector Retest” in the “Operations” menu. After bad cluster is divided into one (or several) area, we may consider to hide this area to avoid incorrect operation in Win 98. This can be achieved by using “Hide Partition” item. We should notice: if we directly hide the partition having bad cluster without formatting it, then some programs with relation to drive letter of the subsequent partition can’t run correctly due to the change of drive letter. For example, the desktop shortcuts of some software can’t find the host program.

The solution is to use “Drive Mapper” item in “Tools”. This item will automatically collects shortcut and registry information and then make right modification. In addition, Disk Manager can also do this job. After partition is hidden, we shouldn’t try to merge the partitions in front of or behind the partition with bad sectors, because these two partitions aren’t physically continuous.

(4) For the condition of hard disk sector 0 damage, it looks difficult to solve, but we aren’t hopeless – as long as we shield the sector 0 and replace it with sector 1. The ideal software to finish this work is the DE tool of PCtools 9.0. We should notice that after the completion of revising sector, partition table information will be written in sector 1 (now, it is used as sector 0) after hard disk is formatted.

(5) We had better not use this method if there are other ways to choose. This way is to carry out low-level format operation on hard disk. There are at least two harmful effects of low-level format: one is that the disc will be worn; the other is that for the hard disk with bad sectors, low-level format will accelerate the proliferation of bad sectors.

(6) Finally, relevant content of BIOS, especially some BIOS with TX chipset should be set properly. They don’t have ability to automatically identify hard disk specification, so, if relevant content of them is improperly set, this will affect the use of hard disk (it may make hard disk can’t be fully utilized or even damaged).

The content above is the solution to hard disk physical damage. But, most of these methods are remedies at the expense of hard disk capacity. When hard disk has bad sectors, if it is not because the hard disk is too old, then this suggests that there is something wrong in the use of it. For example, users defragment hard disk too frequently; too little hard disk memory causes software frequently accessing hard drive.

What’s more, if users ignore dust proofing on hard disk, this will also lead to mechanical failure caused by positioning difficulty of heads. In addition, if hard disk is forced to work under high voltage for a long time, it will be also damaged. Therefore, we had better do prudent operations on hard disk at ordinary times.

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