For example in figure 617 the instructions in the

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Unformatted text preview: in access times is even more dramatic if we compare the times to access a single word. Practice Problem 6.3: Estimate the average time (in ms) to access a sector on the following disk: Parameter Rotational rate Ì Ú× Average # sectors/track Value 15,000 RPM 8 ms 500 Logical Disk Blocks As we have seen, modern disks have complex geometries, with multiple surfaces and different recording zones on those surfaces. To hide this complexity from the operating system, modern disks present a simpler view of their geometry as a sequence of sector-sized logical blocks, numbered ¼ ½ ½. A small hardware/firmware device in the disk, called the disk controller, maintains the mapping between logical block numbers and actual (physical) disk sectors. When the operating system wants to perform an I/O operation such as reading a disk sector into main memory, it sends a command to the disk controller asking it to read a particular logical block number. Firmware on the controller performs a fast table lookup that translate...
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