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When used in a computing environment, parity has to do with the approach that is used to determine if data was lost or compromised in some manner during transfer from a root source to another location. This can include such movements as losing data during an operation, overwriting data, and even when the data is copied and stored in some fashion, such as on disk. It also comes into play when evaluating the transference of data between computer hard drives.
This process of checking data receives its name from the Latin word paritas, which means the equivalent or equal. Since the desired effect of transferring data is to have it arrive at its destination without corruption of any kind, it is the hope that what is received is equal or identical to the original.
Establishing parity involves the insertion of extra binary digits in the transmission of the data. These extra digits are known as parity bits. A single bit is added to a predetermined group of bits that are being moved at the same time. While it essentially rides along with the group of binary bits, it does not actually become a part of the group. Rather, the bit is there to help define the group and hopefully keep the other bits together during the transmission.
The exact structure of the extra bit depends on the group of binary bits it is assigned to travel with. Before the transmission of data takes place, each group of bits is counted to determine the exact number in each group. If the group has an odd number, the parity bit is set to zero. When the group has an even number of bits, it is set to one. Once parity on the originating end is established, the transmission of the data begins.
At the receiving end, each group of bits is again counted to ensure that the entire set completed the journey. This is done by making sure the bits received is an odd number. If the number of bits is an even number, this means that something occurred during the transmission and data was lost from that particular group of bits. An error message is generated, and the end user has the option of trying the transmission a second time.
Parity is simply a means of making sure that what is sent is what is received. Achieving it is the goal with any type of data transmission, and this is most often what actually occurs. If there are continuing issues with achieving it during transmissions, that is a sign that something has been corrupted in the process. At this point, it is important to have an information systems specialist analyze the situation.
Can anyone explain how parity checking takes place?