Alphabetic code
The alphabetic code is based on another ISO standard, ISO 3166, which lists the codes for country names. The first two letters of the ISO 4217 three-letter code are the same as the code for the country name, and where possible the third letter corresponds to the first letter of the currency name.
For example:
The US dollar is represented as USD - the US coming from the ISO 3166 country code and the D for dollar.
The Swiss franc is represented by CHF - the CH being the code for Switzerland in the ISO 3166 code and F for franc.
Numeric code