also involves sending various control and signalling data (TCP) required to reach the destination. This creates a so-called protocol overhead as the additional data does not contribute to the intrinsic meaning of the message. In telephony, number dialing and call set-up time are overheads. In two-way (but half-duplex) radios, the use of "over" and other signaling needed to avoid collisions is an overhead. Protocol overhead can be expressed as a percentage of non-application bytes (protocol and frame synchronization) divided by the total number of bytes in the message. Encodings and data structures (size overhead) The encoding of information and data introduces overhead too. The date and time "2011-07-12 07:18:47" can be expressed as Unix time with the 32-bit signed integer 1310447927, consuming only 4 bytes. Represented as ISO 8601 formatted UTF-8 encoded string 2011-07-12 07:18:47 the date would consume 19 bytes, a size overhead of 375% over the binary integer representation. As XML this date can be written as follows with an overhead of 218 characters, while adding the semantic context that it is a CHANGEDATE with index 1. <?xml version="1.0" encoding="UTF-8"?> <DATETIME qualifier="CHANGEDATE" index="1"> <YEAR>2011</YEAR> <MONTH>07</MONTH> <DAY>12</DAY> <HOUR>07</HOUR> <MINUTE>18</MINUTE> <SECOND>47</SECOND> </DATETIME> The 349 bytes, resulting from the UTF-8 encoded XML, correlates to a size overhead of 8625% over the original integer representation. File systems Besides the files themselves, computer file systems take a portion of the space to store directory names and listings, file names, files' sector locations, attributes such as the date and time of the last modification and creation, how the files are fragmented, written and free parts of the space, and a journal on some file systems. Many small files create more overhead than a low number of large files. See also Slack space Rule of least power Universal Turing machine References Software optimization