Fields can be one of a range of different data types, including: Text, Integer, Real number, Yes/No (Boolean), Date, Time, Sound, and Video.
Key fields allow computers to uniquely identify each record. They contain a unique value for each record. The records in a file are usually sorted by the value of the key field, for example, the ProductID in a stock file.
Each field can only hold one data type at any time. e.g. a field for a date will always, and only, hold a date. Fields can be either fixed or variable in length.
Fixed length fields will always use a certain number of characters for each record. Variable length fields only use the minimum number of characters necessary for each record.
Fixed length fields are faster to search through, but variable length fields use less storage space.