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"How frequently do bit errors occur? If you look at bit error rate in terms of media, some electronic systems experience more errors than others. For instance, optical disk has a higher error rate than magnetic disk. Magnetic tape has a higher error rate than magnetic disk. Fiber optic communications cable and semiconductor memory have a low error rate.
One way to measure bit error rate is in terms of the number of bit errors divided by the total bits transferred. Using magnetic disk as an example, if you were to look at bits coming right off a magnetic disk you would see, on the average, about 1 bit error for every billion bits transferred. If you were to look at bits coming right off an optical disk, you would see a much higher rate of errors, about 1 bit error in every 100,000 bits transferred. Without some form of error detection and correction, most storage devices would be too unreliable to be useful.
Another way to measure bit error rate is in terms of how many bit errors occur in a unit of time. Again, using magnetic disk as an example, if you transfer a million bits per second, on the average, you'd have a bit error every thousand seconds, or every 16.6 minutes. If you transfer a billion bits per second, on the average, you'd have a bit error every second. Currently, some disk drives transfer at the rate of 40 million bits per second, so that a bit error occurs every 25 seconds.
As a general rule, in all electronic devices, transfer rates are increasing as time goes on. Also, errors will occur more frequently in any kind of storage device because manufacturers are squeezing more bits into smaller and smaller spaces. As speed and density increase, error correction becomes a necessity"
"Is error correction done in hardware or software? Error correction can either be done in hardware or software depending upon how fast it has to be done. In most cases, such as magnetic disk drives or semiconductor memory, errors must be detected and corrected "on-the-fly", or, at the same rate as data is being read from the disk. The "on-the-fly" performance requirement usually means the error correction implementation must be done in digital logic (hardware).
In some cases, such as some telecommunications systems where the data rates are relatively low, software implementations of error correction may be fast enough."
"In what ways can error correction be used? Error correction is currently being used to make high capacity storage devices such as magnetic and optical disk and tape reliable. See also How frequently do bit errors occur? Error correction enables higher density recordings. In magnetic disk drives, for example, inexpensive and reliable 2 to 20 GigaByte capacity drives would not be possible without error correction.
Error correction can be used to decrease the price and increase the reliability of DRAM memory modules (SIMMS) because lower-grade DRAM components can be used.
Error correction can be used to extend the battery life of portable computers and other battery-powered electronic devices by allowing a significant decrease in the DRAM refresh rate.
In communications networks, such as ATM, error correction can be used to reconstruct lost or missing packets without the need for retransmission and with no loss of performance. For long-haul lines, frequent retransmission causes severe performance degradation.
In RAID (Redundant Arrays of Inexpensive Devices), error correction can be used to create an arbitrary level of fault-tolerance. Multiple devices can fail with no loss of data or performance.
Error correction can also be used to provide fault-tolerant electronic cabling systems, for example, fly-by-wire aircraft.
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-k
