What technique is used to check if data has been lost or written over during transfer?

The technique used to check if data has been lost or written over during transfer is a checksum. A checksum is a value calculated from a data set, which is then transferred along with the data itself. When the data is received, the checksum is recalculated and compared with the original value. If the two checksums match, it indicates that the data has been transferred successfully without corruption; if they do not match, it suggests that some data loss or alteration has occurred during the transfer process.

In contrast, compression reduces the size of data for efficient storage or transmission but does not inherently verify data integrity. Parity is a form of error detection but is typically used for single-bit errors rather than comprehensive data integrity checks across the entire data set. Encryption secures data by converting it into a coded format; while it protects data confidentiality during transfer, it does not verify data integrity. Thus, the checksum is specifically designed for the purpose of ensuring the integrity of the data during transfer.