In computer science, an error avalanche is the mechanism by which a small problem can become compounded until it eventually becomes a very large one.

For example, if the output of one function (programming) is the input of another, then small round-off errors in the first function can produce much larger errors in the second. If the second function were fed into a third, the problem could grow even larger, until the values produced are worthless.

Another example is in compiling source code. One minor syntactical error early on in the code can produce large numbers of perceived errors later, as the compiler gets out-of-phase with the lexical and syntactic information in the source program.

In computer hardware design, one signal in error can propagate errors throughout a computer very quickly. For example, a power supply voltage that is wrong can cause errors to propagate to many chips. Each chip may detect errors and try to report them close together in time. Error handling systems need to be carefully designed if they are to cope with this and produce meaningful information. This situation has also been called an error storm.

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