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Because of imperfections in the magnetic material.
A lot of people dont realise Bad sectors can easily be created by siting a unit on poor flooring ( floor bounces as you walk over it or heavy traffic vibrates the whole house as it passes ) and the obvious one loosing ones temper and swiping the base unit ,Being drunk in charge of a mouse. and thats not mentioning those that are there at the end manufacture proccess.. heres the links..click here
are incredibly sophisticated, and drives are made under control conditions that would have been unthinkable even a few years back. It isn't really possible to make a drive with tens of millions of sectors and not have the occasional error - possibly the result of a tiny flaw in the extremely thin coating of elctromagnetic material on the drive platters. Manufacturers know this, and they use a clever trick to make new drives look perfect.
On new drives a small number of sectors are reserved as substitutes for any bad sectors discovered in the main data storage area. During testing, any bad sectors that are found on the drive are programmed into the controller. When the controller receives a read or write for one of these sectors, it uses its designated substitute instead, taken from the pool of extra reserves. This is called spare sectoring. In fact, some drives have entire spare tracks available in case they are needed. This is all done without anything being apparent. The result is that the operating system never sees the bad areas, and so it never reports bad sectors on a new drive. They are still there, but they're being hidden. There's nothing underhanded about this - it ensures that nobody gets a problem with brand new drives, or it should.
Bad sector reports on a new drive are almost always an indication of damage that's occurred in use.
I've never bothered to check out how it is done these days but the read/write heads used to literally fly over the disks, they used an electro-magnet (voice coil) to move back and forth and were retracted in order to park/power down. The gap involved between the head and surface was so small that a particle of dust or a hair could cause a major crash. Damage was more often caused by some idiot knocking against a drive (they were as big as washing machines). The disk packs were so large that when a colleague (my ex-boss) forcibly removed one during a DEC maintenance course while it was still running (heads bent & solenoid ripped out), the gyroscopic forces sent him bouncing around the room.
I heard u can use certain software to remove bad sectors.
Does any1 know about this?
As the FE points out hard disk capacity has grown exponentially in the past few years, and the technology has advanced way beyond what was thought possible only five or six years ago. The inevitable result of this is that bad sectors will occur from time to time, it is just a fact of hard disk life. Scandisk will examine your H/D's and mark any bad sectors so that the OS will not attempt to use them again.
Bad sectors are always bad they cannot be repaired.
so thats how they do it. Knew it was done, but now know how it is done. Clever. And as said, means no problem with a new drive.
Spinrite software will thoroughly test your hard drive, read, write and rewite all the sectors something like 100 times and return sectors marked bad to service if they pass its testing. Conversly it will lock out ones that fail.
By running its tests you can completely refresh the sectors of the hard disk, which can supposedly begin to loose their magnetic signal after a long period of zero use. Try click here (note no www) for further info.
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