The single most common hardware fault I deal with relates to failed disk drives; apart from cooling fans these are normally the only components that have moving parts. A disk drive comprises a controller card that contains electronics to manage the data access and the mechanical part, this is basically a collection of platters which rotate with read/write heads hovering a few nanometres above and below. These are what hold the files and the parts that most commonly fail.
Why do they fail ?
What is a bad block, cluster or sector ?
The disk platter is logically broken into small units to enable the data to be passed efficiently. Typically, data is held in bits which hold a value of positive or negative polarity. There are usually 8 bits in a byte, 512 bytes in a sector (block is synonymous with sector) and 4 sectors in a cluster. These values vary with the file system in use but are typical.
Up to a point, bad blocks are a normal function of a disk and the manufacturer will allow a hidden region of the disk to house pointers to known bad blocks. By mapping the blocks to this hidden region, Windows can not allocate the block and it therefore causes no further problem. Problems do occur though when the number of bad blocks exceeds the capacity of the bad block region to house them. The remapping of bad blocks is often called 'repairing' but this is rather a misnomer as the blocks once damaged, are simply hidden from normal operation.
How to avoid or mitigate problems.
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