Published at LXer:

Newer file systems try to keep files from becoming fragmented. Hard disk performance declines with fragmentation. When files are not placed in contiguous blocks, file fragmentation occurs. When a file is spread out over the hard disk, the hard drive "appears" to be slow to the user. The hard drive has to wait for the disk to spin to maneuver the read/write heads over the correct sectors. The lag time causes most users to believe the system is slowing down. The problem is not the computer, but the hard disk.

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