A mnemonic is a memory aid, and most serve as an educational related purpose. Mnemonics are often verbal, something such as a very short poem or word (which may be made up), particularly lists. Mnemonics rely not only on repetition to remember facts, but also on associations between easy-to-remember information and to be remembered lists of data, based on the principle that the human mind much more easily remembers data attached to spatial, personal, or otherwise meaningful information than that occurring in meaningless sequences. The sequences must have some connection to a person's existing semantic associations; if a random mnemonic is made up, it is not necessarily a memory aid.
The word mnemonic is derived from the Ancient Greek word μνημονικ?ς mnemonikos ("of memory") and is related to Mnemosyne ("remembrance"), the name of the Mother of the Muses in Greek mythology. Both of these words refer back to μνημα mnema ("remembrance"). The first known reference to mnemonics is the method of loci described in Cicero's De Oratore.
Visual Mnemonics
Visual mnemonics are very popular in medicine as well as other fields. In this technique, an image portrays characters or objects whose name sounds like the item that has to be memorized. This object then interacts with other similarly portrayed objects that in turn represent associated information.
Arbitrariness of Mnemonics
A curious characteristic of many memory systems is that mnemonics work despite being (or possibly because of being) illogical, arbitrary, and artistically flawed. "Roy" is a legitimate first name, but there is no actual surname "Biv" and of course the middle initial "G" is arbitrary. Why is "Roy G. Biv" easy to remember? Medical students never forget the arbitrary nationalities of the Finn and German. Any two of the three months ending in -ember would fit just as euphoniously as September and November in "Thirty days hath...", yet most people can remember the rhyme correctly for a lifetime after having heard it once, and are never troubled by doubts as to which two of the -ember months have thirty days. A bizarre arbitrary association may stick in the mind better than a logical one.
One reason for the effectiveness of seemingly arbitrary mnemonics is the grouping of information provided by the mnemonic. Just as US phone numbers group 10 digits into three groups, the name "Roy G. Biv" groups seven colors into two short names and an initial. Various studies (most notably The Magical Number Seven, Plus or Minus Two) have shown that the human brain is capable of remembering only a limited number of arbitrary items; grouping these items into chunks permits the brain to hold more of them in memory.
Assembly Mnemonics
In assembly language a mnemonic is a code, usually from 1 to 5 letters, that represents an opcode, a number.
Programming in machine code, by supplying the computer with the numbers of the operations it must perform, can be quite a burden, because for every operation the corresponding number must be looked up or remembered. Looking up all numbers takes a lot of time, and mis-remembering a number may introduce computer bugs.
Therefore a set of mnemonics was devised. Each number was represented by an alphabetic code. So instead of entering the number corresponding to addition to add two numbers one can enter "add".
Although mnemonics differ between different CPU designs some are common, for instance: "sub" (subtract), "div" (divide), "add" (add) and "mul" (multiply).
This type of mnemonic is different from the ones listed above in that instead of a way to make remembering numbers easier, it is a way to make remembering numbers unnecessary (by relying on some external way to tie each mnemonic to a number).