This document defines common units of digital storage, including bits, bytes, words, and double words. It explains that a bit is the smallest unit that can store 1 or 0, while a byte contains 8 bits. A word contains 16 bits, which is equivalent to 2 bytes. Finally, a double word is 32 bits long, consisting of 2 words or 4 bytes. These basic units are used to measure digital storage capacity in computers.