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I want to ask about this : bad sectors ,what are the sectors, when they become bad, and what are the problems caused by having them and what to do when having bad sectors.

Regards !

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A sector is the most basic unit of mass storage. In platter hard disks and floppies, it's a fixed-size fraction of a track, which is defined as a series of circular paths, approximately the width of a read/write head, in which data can be written and from which it can be read. Generally, in FAT (FAT12, FAT16, and FAT32) systems, a sector is 512 bytes in size, and the number of sectors in a track is defined by the storage density of the media.

Worth noting that on a Solid State Drive (SSD), the flash RAM is organized in virtual sectors for compatibility with firmware and software that expects to find data stored in that kind of chunks.

Sectors are usually organized in blocks, which are one or more (usually a power of 2) sectors that are handled as a unit. Because of this, you'll sometimes see your OS or disk management system referring to bad blocks rather than bad sectors.

A bad sector (or bad block) is a sector or block which, for one reason or another, doesn't read back the same data that was written there. This can happen due to physical damage (computer dropped, causing the heads to skitter across the platters), or due to wear (older drives tend to increase the number of bad sectors as the media age, probably because of an accumulation of very minor physical damage points). The operating system or storage device firmware detects these and marks them, so they won't be reused at the risk of data loss; this is what you'll see in a disk health report (S.M.A.R.T. report or similar) as bad sectors or bad blocks.

Usually, the only thing you need to worry about relative to bad sectors or bad blocks is if the number starts to increase rapidly, or there's a sudden increase even if the number then remains steady. Running regular S.M.A.R.T. reports can help with tracking this information, and give you warning when a drive may be aging enough to require backup and replacement -- before it dumps a bunch of your favorite photos or emails from your significant other into the bit bucket.

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In every hard disk, CD, pendrive, etc. data is categorized and saved in clusters. Each of these is called a sector. Sectors are called bad when the OS is not able to access them.

There are two types of bad sectors

  1. physical (hardware)
    Physical bad sectors occur when some physical damage happens to the disk or it it worn due to use. Caused mainly due to imperfect manufacturing techniques. It is unrepairable.

  2. logical (software)
    Logical bad sector are sectors on the hard drive that appear to not be working properly. These are caused by software issues. This type can be corrected using software or low-level formatting.

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