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IBM System/7 Functional Characteristics - All about the IBM 1130 ...

IBM System/7 Functional Characteristics - All about the IBM 1130 ...

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FILE ORGANIZATIONEach surface of each disk contains 204 tracks. The tracks that are related to each o<strong>the</strong>r in<strong>the</strong> vertical plane on a single disk are considered to form a cylinder, as shown in Figure15-2. The corresponding cylinders on both disks have <strong>the</strong> same cylinder number.Cylinders are numbered 0 through 203. Cylinder 203 is reserved for customer engineeruse. Cylinders 1 through 3 are used as alternate cylinders if a track in cylinders 4 through202 is found defective. Cylinder 0 and cylinders 4 through 202 are <strong>the</strong> normal datacylinders.Sectors within a track are identified by <strong>the</strong>ir physical position on <strong>the</strong> track with relationto <strong>the</strong> index mark and by <strong>the</strong> surface of <strong>the</strong> disk on which <strong>the</strong>y reside.204 cylindersTrack 0Track 0Track 0Track 0One cylinderOne cylinderFigure 15-2. Cylinder conceptTrack FormatEach track is divided into 24 sectors, as shown in Figure 15-3. Each sector in a track hasits own individual address and is made up of an address mark, sector identifier, data field,and some gaps.Index Mark: A mark that is fixed for each disk and provides orientation information to<strong>the</strong> module circuits. It is <strong>the</strong> starting point for every track.AM (address mark): A specially written group of bits used to indicate <strong>the</strong> start of a newsector.15-4 GA34-0003

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