What is the cyclic redundancy check

Modern technology uses a lot of math. Most machines, especially computers use numbers and mathematical equations to run. Computers use a lot of different mathematical functions to run properly. One of the functions that computers may use is cyclic redundancy check or CRC.

What is a cyclic redundancy check

A cyclic redundancy check (CRC) is an error detection mechanism. It is used to make sure that the data that a person is trying to read from something such as a CD, DVD, or hard disk is the actual correct data. Correct data means the data that is really written on the CD, DVD, or hard disk.

A cyclic redundancy check inputs a stream of any length of data and produces a value of a certain space as its output. The actual term cyclic redundancy check is used to symbolize the function or the output of the function.

The purpose of a cyclic redundancy check

The purpose of a cyclic redundancy check is to help maintain the integrity of information and data across not very reliable storage media and noisy channels.

How does a cyclic redundancy check work

A cyclic redundancy check takes a block of data that is going to be written to the CD, DVD, or hard disk, calculates a checksum, writes the number with all the original data to the CD, DVD, or hard disk. Later, when the data is going to be read and the same calculation happens, if a different number comes from the calculation then there is an error and the data that was read was not the same data that was originally written.

The operation

The computation of a cyclic redundancy check is actually similar to a long division problem. With this particular program, the quotient is removed and the remainder actually becomes the result. The arithmetic that is used is the carry-less math of a finite field. In computing a cyclic redundancy check, the remainder must always be less than or equal to the divisor in length. This then determines how long the result is to be.

When errors happen and what to do if an error occurs

Since cyclic redundancy checks occur each time a person reads a CD, DVD, or hard disk, a lot of CD and DBD burning programs include a read pass right after writing to make sure that the data is written properly. A checksum error could happen in several circumstances. If there is dirt, dust, or other obstructions in the DVD or CD writer it can interfere with the workings of the laser and bad data could be written. There could also be dirt or dust in the reader which may not allow the DVD or CD's reader to not read the media correctly.

Another reason that an error could occur is if a problem was encountered while the burning device was trying to write the DVD or CD. If there was a problem, the wrong data could have been written. Poor quality CDs or DVDs could also be the reason for the error. Even the smallest of errors, one that a person cannot even see, on the DVD or CD could cause the actual CD or DVD to not allow the data be written on them. Bad writing or reading alignment could cause an error. Data needs to be put on a CD or DVD in a circle. If the alignment is off, even a little bit, then the writing and reading cannot occur correctly.