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SMR or Shingled Magnetic Recording (as used in an SMR drive) is a method of increasing the recording density on a hard drive by writing each track so as to partially overlap the previous one, in the manner of roofing tiles (or shingles). This means that previously written data cannot be overwritten as it would partially overwrite both the previous and following data tracks. If data is updated it must be appended to the existing data, and either the disk controller or the operating system must keep track of its new location on the disk, and also remember that the old copy is now stale. Once a contiguous block of data of a certain size has been marked as stale, it can all be overwritten from the start of the block with more shingled data tracks. SMR drives are best suited to applications such as archivng, where data is rarely updated, or mostly updated in large chunks.