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Dale - Computer Science Illuminated 156

Dale - Computer Science Illuminated 156 - sectors and each...

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Track A concentric circle on the surface of a disk Sector A section of a track Block The information stored in a sector 5.2 Stored-Program Concept 129 Block Track Sector (b) A single disk (a) A hard disc drive Arm Spindle Cylinder Read / write head Figure 5.5 The organization of a magnetic disk Disks come in several varieties, but they all use a thin disk made out of magnetic material. The surface of each disk is logically organized into tracks and sectors . Tracks are concentric circles around the surface of the disk. Each track is divided into sectors. Each sector holds a block of infor- mation as a continuous sequence of bits. (See Figure 5.5.) Although the tracks nearer the center look smaller, each track has the same number of
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Unformatted text preview: sectors, and each sector has the same number of bits. The blocks of data nearer the center are just more densely packed. The actual number of tracks per surface and the number of sectors per track vary, but 512 bytes or 1024 bytes are common. (The power of two strikes again.) The location of the tracks and sectors are marked magnetically when a disk is formatted; they are not physically part of the disk. The read/write head in a disk drive is positioned on an arm that moves from one track to another. An input/output instruction specifies the track and sector. When the read/write head is over the proper track, it waits...
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