A simple sum of all bytes (or words) in a block
of data, taken modulo 256 (or 65536).  Used to
verify data integrity.

(CRC) Cyclic Redundancy Code
Like a checksum, but using a complicated formula
that avoids offsetting errors.

(ECC) Error Checking and Correction
Like a CRC, but containing more information.
With an ECC, it is possible to detect all errors
and to correct all single-bit and some multiple-
bit errors.