The disk firmware silently corrects detected errors when a read is requested by the operating system. Each sector consists of the data itself plus additional data to aid with location, error detection and error correction.Įrror correction uses a mathematical technique to add a measure of redundancy to the data during writing enabling both the detection and correction of a limited number of bit errors during a subsequent read. Data can only be read or written as a sequence of complete sectors. Note, this error rate rises rapidly for failing disks.ĭisks are segmented into blocks of data typically called ‘sectors’. All this is achieved in an environment exposed to vibration and varying temperatures.Įrrors are a natural consequence and the design of a modern disk accounts for this with error correction, retries and remapping to reduce the uncorrected bit error rate around 1014 or higher for enterprise disks. It also requires great mechanical precision to locate the read head. Hard drives are extraordinary devices rapidly returning vast quantities of uncorrupted data while relying on quantum magnetic effects to interrogate the magnetic state of vanishingly tiny areas of magnetic surface. Typically a CRC error is reported when performing an image backup, or when performing a chkdsk surface scan.

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