Naked eye – even a one-bit error can cause a CRC calculation to fail.īad Write Alignment: it’s fairly obvious that on CDs andĭVDs data is written in a circle on the media. These types of flaws may not be visible to the Perhaps there’s aįlaw in the physical media.
Problem while writing, it could have written the wrong data.ĭirt in the Writer: dust or other obstructions in a CD orĭVD writer can interfere with the laser and cause the bad data to be written.īad Media: poor quality media, particularly CDs and DVDs,Ĭan sometimes “not take” the data that’s written to them. There are several ways that a checksum error could happen:Ī Bad Write: if the device that wrote the media had a Programs will include a read pass immediately after writing, to ensure that the When the data is later read, that same calculation happens, and if aĭifferent number results, then an error is declared – the data read was not theĬRC checks happen each time you read the media. Results in a number), and writing that number, along with the original data, to Media, calculating a checksum (basically some math involving all the data, that When a CRC check fails, there are several possibilities and places toĪ CRC works by taking a block of the data that is about to be written to the Mean that the data you read is in fact the data that was written.
Media, such as hard disks, CDs and DVDs, is actually correct. A “Cyclic Redundancy Check”, or more commonly just “ CRC”, is an errorĭetection mechanism that makes sure that the data you’re trying to read from
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