Skip to main content

error rate

error rate
1. of a communication channel. The frequency with which errors or noise are introduced into the channel. Error rate may be measured in terms of erroneous bits received per bits transmitted. For example, one or two errors per 100 000 bits might be a typical rate for a narrowband point-to-point line. The distribution of errors is usually nonuniform: errors tend to come in bursts (see burst error). Thus the error rate of a channel may be specified in terms of percentage of error-free seconds. Frequently an error rate is expressed as a negative power of ten: an error rate of one bit per 100 000 would be expressed as an error rate of 10−5.

Another method of presenting error rate is to consider the errors as the result of adding the data signal to an underlying error signal. The extent of error can then be expressed as the entropy of the error signal, or, in the case of physical signals, as the ratio of the strengths of the two signals – the signal-to-noise ratio – expressed in decibels.

2. of a data storage subsystem. A measurement of the proportion of errors occurring in data transfers to or from the storage medium. It is usually expressed in terms of the average number of bytes or bits of data transferred per error, e.g. 1 error per 109 bytes, although it can also be useful to express the rate as the average time between errors for typical usage of the subsystem, e.g. 1 undetected error in 6 weeks at 10% duty cycle.

The error rates most frequently specified relate to the following.

A transient (or recoverable) read error occurs during reading and can be recovered by the error recovery procedure prescribed for the storage subsystem (see error recovery). Where the recording format provides sufficient redundancy to allow some error to be recovered on-the-fly, i.e. without re-reading the data, it is necessary to define also the raw error rate, which is the rate that would be perceived if on-the-fly error recovery was not applied.

A permanent (or irrecoverable) read error cannot be recovered by the prescribed error recovery procedure.

A transient (or recoverable) write error occurs during writing and can be recovered by the error recovery procedure prescribed. It is desirable, though not easy, to distinguish two components of this error rate: errors attributable firstly to flaws in the media and secondly to failings of the device (one reason for the difficulty is that these tend to interact).

A permanent (or irrecoverable) write error cannot be recovered by the prescribed procedure. Again it is necessary to distinguish between media flaws and device errors: rather than give a figure for the latter it is usual to regard each occurrence as a fault to be accounted for in the failure rate of the device (see hardware reliability).

An undetected error is an error that is not detected by the storage subsystem, presumably because of some inadequacy in the error check facilities defined by the format or in their implementation, or because of errors occurring outside the ambit of these facilities (see data integrity).

Cite this article
Pick a style below, and copy the text for your bibliography.

  • MLA
  • Chicago
  • APA

"error rate." A Dictionary of Computing. . 21 Mar. 2019 <>.

"error rate." A Dictionary of Computing. . (March 21, 2019).

"error rate." A Dictionary of Computing. . Retrieved March 21, 2019 from

Learn more about citation styles

Citation styles gives you the ability to cite reference entries and articles according to common styles from the Modern Language Association (MLA), The Chicago Manual of Style, and the American Psychological Association (APA).

Within the “Cite this article” tool, pick a style to see how all available information looks when formatted according to that style. Then, copy and paste the text into your bibliography or works cited list.

Because each style has its own formatting nuances that evolve over time and not all information is available for every reference entry or article, cannot guarantee each citation it generates. Therefore, it’s best to use citations as a starting point before checking the style against your school or publication’s requirements and the most-recent information available at these sites:

Modern Language Association

The Chicago Manual of Style

American Psychological Association

  • Most online reference entries and articles do not have page numbers. Therefore, that information is unavailable for most content. However, the date of retrieval is often important. Refer to each style’s convention regarding the best way to format page numbers and retrieval dates.
  • In addition to the MLA, Chicago, and APA styles, your school, university, publication, or institution may have its own requirements for citations. Therefore, be sure to refer to those guidelines when editing your bibliography or works cited list.