When a module's command finishes, the output objects (of memory types) have to be saved on disk for future use. For example, they can be the input of another module's command. Data may be saved on disk also (or read from disk) when the module is run into an interpreter such as XMegaWave2, although in this case modules communicate with memory type structures.
This shows that external type objects are needed; they are files written in a predefined format. MegaWave2 can use some well-known formats available in the public domain, especially to carry the different image memory types. When no satisfying standard is available to match a given memory type, a specific format is used. Notice that, whereas there is only one memory type associated to an object, an object of a given memory type may be represented on disk with various file types.
Conversions between some formats are available: you may load an object written
in a file type which is different from the regular one used for the memory type of your object. Depending on the case, you may however lose precision in your data
(in that case, a warning message is send).
For output ojects, MegaWave2 chooses a default file type to write the data.
You can modify this choice using the system option
-ftype (See Volume one: ``MegaWave2 User's Guide'').
A short description of the file types is given in the next sections about the different memory types.