Magnetic disks organize their data – as opposed to random access memories (which arranges in bytes or in small groups of 2 to 8 bytes) – in data blocks (such as 512, 2048 or 4096 bytes), which is why this method is called block-based addressing . It only whole data blocks or sectors can be read and written by the PC hardware.

The reading blocks are specified by the linear sector number. The hard drive knows where the block is, and reads or writes a copy on request. When writing blocks these are first provided with error correction information.

They are subjected to modulation: GCR were earlier, MFM, RLL common nowadays have PRML and recently replaced EPRML this, then reading the write head, which is assigned to the information bearing surface, the track signal and performs the positioning by fine. This includes on the one hand, to find the right track to meet exactly centered to the other this track as shown by Dell Computer Repairs Sydney.

If the read-write head stable on the track and has the correct sector under the read-write head, the modulation block is written with suspected incorrect position of the writing process should be stopped immediately to prevent neighboring tracks (partially irreparable) are destroyed.

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