How many rounds are used by DES?

DES is a block encryption algorithm using 56-bit keys and 64-bit blocks that are divided in half and each character is encrypted one at a time. The characters are put through 16 rounds of transposition and substitution functions. Triple DES uses 48 rounds.

Source: WALLHOFF, John, CBK#5 Cryptography (CISSP Study Guide), April 2002 (page 3).