This looks a little silly, but it shows the checksum is a kind-of-copy squeezed into a smaller space. We send the text as well a second copy, the checksum, with the letters "squeezed" to save space, like this: Say we haveĪ line of text, Hello there!, that we transmit. Here is a visual depiction of what we want to do. There is one useful (but limited) technique that does this. That would also tell us where to correct an error when it occurs. If we are really bold, we should find a version of checksum The transmitted checksum can be compared with the transmitted data What happens in practice is that the data is sent with a small extra number, called its checksum, that somehow restates the data in an abbreviated, ``squeezed-in'' form. If we send data twice, it is twice as large and takes twice as long to transmit. (But what if the data was corrupted exactly the same way every time? There is never 100% confidence.) One way to verify correct transmission is to send the same data two or three times - if the data are received identically, we are confident that the transmission is error free. All data that is moved must be checked at the receiving end to verify, with over 99% confidence, that the data is correct.
When information (data) is moved between computers, it can become corrupted, due to physical problems, e.g., static on the transmission wire.
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