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A Practical Introduction to Data Structures and Algorithm Analysis

A Practical Introduction to Data Structures and Algorithm Analysis

A Practical Introduction to Data Structures and Algorithm Analysis

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284 Chap. 8 File Processing <strong>and</strong> External SortingBoom(arm)PlattersSpindle(a)Read/WriteHeads(b)TrackFigure 8.2 (a) A typical disk drive arranged as a stack of platters. (b) One trackon a disk drive platter.Intersec<strong>to</strong>rGapsSec<strong>to</strong>rs(a)Bits of <strong>Data</strong>(b)Figure 8.3 The organization of a disk platter. Dots indicate density of information.(a) Nominal arrangement of tracks showing decreasing data density whenmoving outward from the center of the disk. (b) A “zoned” arrangement with thesec<strong>to</strong>r size <strong>and</strong> density periodically reset in tracks further away from the center.arrangement is illustrated by Figure 8.3a. Disk drives <strong>to</strong>day actually group tracksin<strong>to</strong> “zones” such that the tracks in the innermost zone adjust their data densitygoing out <strong>to</strong> maintain the same radial data density, then the tracks of the next zonereset the data density <strong>to</strong> make better use of their s<strong>to</strong>rage ability, <strong>and</strong> so on. Thisarrangement is shown in Figure 8.3b.In contrast <strong>to</strong> the physical layout of a hard disk, a CD-ROM consists of a singlespiral track. Bits of information along the track are equally spaced, so the informationdensity is the same at both the outer <strong>and</strong> inner portions of the track. To keep

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