Hard Disk Drive Systems

HDD Basics

Hard disk drive (HDD) is used for permanent storage and quick access. Usually they are inside the PC but external drives are also available It has one or more platters, or disks, put together above each other to spin together inside the sealed enclosure that has firmware to control read and write of data to the drive and to communicate with the motherboard. The top and bottom of each disk have a read/write head that moves across the disk surface as all the disks rotate on a spindle. Read/write heads are controlled by actuator, which moves heads across the disk surfaces. Disk surfaces are covered with magnetic medium to hold data by magnetizing. Each disk surface is divided into concentric circles, called tracks and each track is further divided into 512-byte segments called sectors. All the tracks that are the same distance from the center of the platter is called as one cylinder. Low-level formatting of hard disk is done by marking track and sector by manufacturer. The total number of sectors tell the capacity of drive and is usually in GB or TB (terabytes, 1 TB=1024GB).Logical block addressing (LBA)  is sequential numbering system used by BIOS and the operating system to address all sectors.

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