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Data Verification
It is important to prevent errors occurring in data. Verification is used to prevent errors occurring when data is copied from one medium to another. (eg paper to disk, disk to disk, memory to disk)

Methods used for verification...

Double keying Used to check for transcription errors. The data is entered twice (by two different people). The computer will only accept the data for processing if the two versions are identical.
Visual check Checking for errors by looking through the data. Eg Proof-reading a typed document.
Parity Used to check for transmission errors over networks or between memory and disk.

An extra bit is added to each binary number before it is transmitted. Even parity systems make sure that each number has an even number of '1' bits.

After transmission, each binary number is checked to see if it still has an even number of '1' bits.

Example (Even parity)

If 11010111 is transmitted ...(6 '1' bits)
and 11010011 is received ... (5 '1' bits)
then the computer knows a corruption of the data has occurred.

 
Exercise : Data Verification
of data is checking that data has been copied from one medium to another correctly.

Methods used for verification are...

  • - proof-reading copied data.
  • - This checks for errors. Data is entered twice and only accepted if the two versions are identical. 
  • - This checks for errors. An extra parity bit is added to every binary number before transmission so that all numbers have an even number of '1'-bits.(even parity) The data is re-checked when received. 
(Green indicates success)